when the first exhaust line 15 a is connected to the air source side and the flow rate of the air supplied between the mounting table 11 and the wafer w can be properly controlled by means of the throttle valve 17 a in addition the first exhaust line 15 a is also connected to an inlet of the second air flow path 13 b via a second exhaust line 15 b also a third electromagnetic valve 18 is installed on the second exhaust line 15 b and the first and the third electromagnetic valve 16 and 18 are operated together when necessary further a vacuum sensor 19 having a switch is connected to the first exhaust line 15 a to detect a vacuum level between the mounting table 11 and the wafer w when its switch is on thus to vacuum chuck a wafer of 300 mm on the mounting table 11 hermetically the first and the third electromagnetic valve 16 and 18 are actuated whereby the first and the second flow path 13 a and 13 b are allowed to communicate with the vacuum pump via the first and the second exhaust line 15 a and 15 b concurrently the vacuum sensor 19 detects a vacuum level between the mounting table 11 and the wafer w to lift up the wafer w from the mounting table 11.