To provide a technique capable of staring generation, even when a fluid force is small.

The generator (1000) comprises impeller blades (1200) rotating in response to the fluid force from fluid, a generator motor (100), a flowing rate measuring section (1130), a rotation number measuring section, and a control unit (200). When at least the flowing rate or the rotation number remains within a specified low range at the start of the generator motor, the control unit (200) operates the generator motor as a motor to increase the rotation number of impeller blades and then operates the generator motor as the generator.