A cooler includes: a narrow flow path that has a narrow cross-sectional area; a wide flow path that is connected to a downstream side of the narrow flow path, is in thermal contact with a heating body, and has a wide cross-sectional area; and at least one rectifying piece that is provided in an upstream portion of the wide flow path that is an upstream side from a position being in thermal contact with the heating body. A fluid refrigerant flows through the narrow flow path and the wide flow path, and heat generated by the heating body is radiated. The rectifying piece includes: a single first angle portion that protrudes toward the upstream side; and a first surface and a second surface that join at an acute angle to form the first angle portion.