To form a diaphragm along an inner wall of a recessed part and an external wall of a projection part in a condition in which an air chamber is compressed, resolve unnecessary deformation of the diaphragm, shorten a pressurizing time, and improve pressurizing force by arranging a case having the recessed part and a driving body having the projection part.

When current-carrying to a motor part 1 is carried out, a rotor 7 fixed to an output shaft 5 is rotated. When a driving body 37 nearest approaches the motor part 1 through a driving body pin 43 engaged with a diagonal shaped recessed groove 45 of the rotor 7, an air chamber 31 formed by a diaphragm 11 fixed to the driving body 37 is expanded. As a result, pressure in the air chamber 31 is reduced,. air accumulated in an intake chamber 35 is made to pass an intake hole 23 bypassing an intake passage 27, an intake valve 19 is pushed and opened, and the air flows into the air chamber 31. In this time, a recessed part 39 is formed on a ventilation cover 132, a projection part 41 is formed on the driving body 37, and thereby, the diaphragm 11 is formed along an inner wall of the recessed part 39 and external wall of the projection part 41 os as to prevent unnecessary deformation.