each other then the lower end portion of the eccentric rotation shaft 13 is brought near to the center of the rotary body 24 and guided by the guide groove 27 and the guide inlet 26 to be introduced and inserted into the hole 25 therefore a worker need not insert the lower end portion of the eccentric rotation shaft 13 into the hole 25 while confirming the hole 25 as in the related art pump and the eccentric rotation shaft 13 can be automatically inserted this enables the eccentric rotation shaft to be easily assembled and the working efficiency can be enhanced in this state when the rotary body 24 is rotated with the rotation of the motor 19 the lower end portion of the eccentric rotation shaft 13 will be pivoted inside the hole 25 resulting in an eccentric rotation this will cause the pivoting motion of the pivotable member 6 thereby to move the lower end portions of the diaphragms 4 up and down when the lower end portion of one of the diaphragms 4 for example is moved downward negative pressure is generated inside the diaphragm 4 and the vent valve body 12 is tightly fitted to the inner wall face 11 a of the annular concave groove 11 in this manner the vent valve section v 2 is closed and the air intake valve body 8 opens the through hole 9 in other words the air intake valve section v 1 is shifted into an open state and air is introduced from the.