machine further comprises a post 12 held upright in the machining vessel 1 an air pressure supplying block 13 which is lifted along the post 12 by a drive unit 14 a solution level detector which is located at a predetermined distance from the air jetting holes 7a through 7e formed in the air jetting unit 7 which is secured to the air jetting unit 7 a signal line 18 for transmitting the output of the detector 17 to the drive unit 14 a pump 15 for producing the air pressure which is supplied to the air pressure supplying block 13 a control valve 16 for adjusting the air pressure thus produced and a dam 11 board for determining the level of the machining solution in the machining vessel 1 in the electrical discharge mac air pressure produced by the pump 15 is adjusted optimully by operating the control valve 16 and supplied through the air pressure supplying block 13 and the air jetting unit 7 to the air jetting holes 7a through 7e thus forming the stream of air 8 over the machining solution 4 the stream of air 8 thus formed is sucked together with the decomposed gas 5 and the oil mist 6 by the air sucking unit 9 provided on the opposite side so that the decomposed gas.