of alarm signal a1 is given the alarm 47 transmits alarm sound repeatedly and intermittently and operation of the automatic door 41 is stopped under this condition fig1 m shows processing of opening slip trouble mode although the alarm sound of specific pattern is transmitted for the specified time mode turns to the close stand by mode shown in fig1 e as there is no need to stop operation of the automatic door 41 fig1 n shows processing of closing slip trouble mode although the alarm sound of another specific pattern is transmitted for the specified time mode turns to the open stand by mode shown in fig1 a as there is no need to stop operation of the automatic door 41 as described above this automatic door 41 detects break of the belt 43 stops operation and transmits alarm slipping of the belt 43 is also detected at an early stage and alarm is transmitted the operator can guess the cause of trouble easily since the alarm transmission is made in specific pattern depending on each cause of trouble as the alarm means lamp buzzer and crt display may be used for example the alarm which can identify and notify brake defect is preferable in particular other embodiments may include the arrangement to judge door position from speed pulse signal so as to eliminate door position sensors ls1 ls2 may include infrared ray type sensors or radar type sensors in place of the mat switch ms or may include the arrangement to comprise the central control unit 50 with hardware circuits without using the microcomputer 51 after all by the brake apparatus of the above described automatic door.