A diaphragm pump 1 has a base block 2, a diaphragm 8 and a drive unit for driving the diaphragm to reciprocate. The base block 2 has three or more liquid flow paths, each having three recesses 23 through 25 or more recesses. The diaphragm 8 and the respective recesses 23 through 25 define a plurality of valve chambers and the metering chamber. The drive unit includes: pressing rods 73 through 75 arranged corresponding to the respective recesses with the diaphragm interposed therebetween; and a pressing member drive controller adapted to execute a liquid discharging operation and a liquid sucking operation at a predetermined timing defined for each of the pressing rods, in which in the liquid discharging operation, each of the pressing rods is moved toward the respective recesses so as to gradually decease the volume of the respective valve chambers and the metering chamber and eventually hermetically seal the metering chamber; while in the liquid discharging operation, each of the pressing rods is moved away from the respective recesses so as to gradually decease the volume of the respective valve chambers and the metering chamber.