PURPOSE: To eliminate necessity for a particular means for absorbing a pulsation by extending/contracting a plurality of dampers, and the like to suppress the pulsation of delivered liquid while extending/contracting a plurality of diaphragms according to right/left sliding a sliding shaft.

CONSTITUTION: When a sliding shaft 22 of a tandem diaphragm pump 21 is slid rightward, liquid, with which a pump chamber 28 of a chamber 26' is charged, is delivered from a delivery port 36 of a pump main unit 25 to pass through a delivery value 32, and also charging the pump chamber 28 of the chamber 26 with the liquid passing a suction valve 31. When a pressure of liquid 8 in the pump chamber 28 in the compressed chamber 26' rises, since the volume of a damper 35' is compressed, a pulsation of the delivered liquid is suppressed. On the other hand, when the sliding shaft 22 is slid leftward, the liquid is delivered and charged by reverse action similar to the above, and also a pulsation of the delivered liquid can be suppressed by a damper 35.