To provide a power source device for easily reducing the size and cost, by restraining the occurrence of operational failure, by minimizing a factor of causing clogging in a supply system for supplying air to a fuel cell stack.

This power source device has the fuel cell stack 2 of laminating a plurality of cells of a fuel cell, and an air pump 4 for supplying oxidizing agent gas to the fuel cell stack, and also has a pressure detector 11 detecting delivery pressure of a pump, a current detector 12 detecting a load current of the fuel cell stack, and a rotating speed detecting means detecting a rotating speed of the pump. A storage part 13 stores information on a target supply flow rate to the fuel cell stack of the oxidizing agent gas and information on the relationship between the rotating speed of the pump, the delivery pressure of the pump and the target supply flow rate. The rotating speed of the pump is controlled by a control part 10 based on the information stored in the storage part and a detecting result of the pressure detector, the current detector and the rotating speed detecting means.