A pump system (1) includes: a triple-gear pump which pressurizes a fluid using three gears (3a, 3b and 3c); an outlet flow path (R4) which guides the fluid from a first pressure-increasing portion (A) to an outlet; a first flow path (R1) which guides the fluid from the first pressure-increasing portion to a second pressure-increasing portion (B); a second flow path (R2) which guides the fluid from the second pressure-increasing portion to the outlet flow path; a third flow path (R3) connected to the first flow path and the second flow path; a first valve device (4) provided in the first flow path; a second valve device (7) provided in the second flow path, and a control device (8) which controls the first valve device. When the first pressure-increasing portion and the second pressure-increasing portion are switched from a parallel state to a series state, the control device causes the first valve device to open after the second valve device is closed.