To provide a diaphragm pump device of a gas detector and a portable explosion-proof gas detector, capable of providing excellent startability, while saving electric power.

This diaphragm pump device of the gas detector is constituted so that a diaphragm is reciprocated via a driving rod by driving a driving DC motor (hereinafter referred to as "a motor") in the normal rotation direction in an ordinary driving state, and is stopped in a low strain position small in a strain quantity of the diaphragm by stopping of the motor. When starting the motor, a preliminary driving process and an ordinary driving process of driving the motor in the normal rotation direction by normal rotation driving voltage of a predetermined size, are performed, and in the preliminary driving process, the motor is driven in the reverse rotation direction by reverse rotation driving voltage smaller than the normal rotation driving voltage, and the diaphragm is deformed in the inverse direction of the deforming direction of becoming maximum in the strain quantity in the first place in the ordinary driving process. The portable explosion-proof gas detector includes the diaphragm pump device.