A pump device is realized, which accurately detects a flow rate of a pump, performs real-time control of the flow rate, and thus can suppress a flow rate error caused by occurrence of pulsation. Control of a pump rotation speed by a pressure sensor has low responsiveness in a low pressure region, and a correlation between a pressure and a flow rate is incomplete in a high flow rate region. With this taken into consideration, a flow rate sensor 10 is disposed at an outlet port 9 of a second pump 4. A position detection sensor 14 detects a point where a first pump 3 is shifted from a suction mode to a discharge mode. Moreover, the flow rate sensor 10 detects that there is no discharge from the pump 3, and that there is discharge from the pump 4 alone. Accordingly, a controller 15 sets a rotation speed of a motor 12 to a speed double the previous speed (double the normal rotation speed). When the flow rate sensor 10 detects an increase in the flow rate at the outlet port 9 of the second pump 4, the controller 15 returns the rotation speed of the motor 12 to a normal rotation speed. The rotation speed of the motor 12 is controlled by accurate flow rate detection by the flow rate sensor 10. Thus, occurrence of pulsation can be suppressed.