According to buddhism, do demons exists? I have heard a lot about this kind of things called demons, satan, evil spirits from other religion. But is their any mention in buddhism about existance of such creatures or spirits?
According to Buddhism Demons exist. The Four Great Kings in the Cāturmahārājika Heaven keep watch over us of harm from these demons. There are a handful of (few) good demons too who have seen the Dhamma.)  These four Devas are Virūpākṣa (he who sees all), Dhṛtarāṣṭra (he who upholds the realm), Virūḍhaka (he who causes to grow), and Vaiśravaṇa (Kubera) (he who hears everything).  All four Devas serve Śakra, the lord of the devas. All demons have spontaneous birth (opapatika) like the Davas and the Petas (Hungry Ghosts). You may know by now that there are four kinds of birth - namely, egg-born (andaja), womb-born (julabuja), moisture-born (samsedaja), and spontaneous birth (opapatika).

There are four lower planes of existance = Niraya = devoid of happiness. There are four kinds of niraya - namely, woeful state (apaya / hell), the animal kingdom, the plane of Petas (hungry ghosts) and the plane of Asura-demons (Titans). None of these states is eternal. According to their unwholesome / unskillful kamma beings may be born in such woeful states. Departing from those states, they may be born in blissful states according to their past good kamma. In the sense-sphere (kamaloka) the human plane and the six celestial planes are regarded as blissful states. They too are not eternal.

Devil is referred to as MARA, in the scriptures. Mara means killer. He is the personification of the force that kills virtue and also kills existence. His armies are poised to attack all persons; they even tried to overcome the Buddha on the night of his enlightenment. But Mara is a post that is been held by a person.  If you are attached to the six senses, you are in the Mara (Devil)s grasp (a firm hold or grip). He is a tempter, distracting humans from practicing the spiritual life by making mundane things alluring, or the negative seem positive.

At the time of Kakusandha Buddha – our Gautama Supreme Buddha’s chief disciple, Ven. Maha Moggallana was the Mara, chief of demons, lord of the lower worlds.  Kakusandha is the fourth of the Seven Buddhas of the last 91 Kalpa (Aeons), and the first of the five Buddhas of the present kalpa. The present day Mara is his sister’s son (nephew). When someone talks about “God’s grace” and “God’s mercy”,  it can more likely be that the blessings are of Mara and his hosts. This is possible. As the great jealous one, Mara has the power to bestow blessings on his hosts and subjects.

Getting back to the subject of Demons, here is a question &amp; answer session that once took place between a King (Milinda) and an Arahant ( Ven. Nâgasena):


  'Venerable Nâgasena, are there such things as demons (Yakkhâ) in the world?'
  'Yes, O king.'
  'Do they ever leave that condition' (fall out of that phase of existence)?
  'Yes, they do.'
  'But, if so, why is it that the remains of those dead demons are never found, nor any odour of their corpses smelt? '
  Their remains are found, O king, and an odour does arise from their dead bodies. The remains of bad demons can be seen in the form of worms and beetles and ants and moths and snakes and scorpions and centipedes, and birds and wild beasts.'