A cooler for cooling a semiconductor module includes a top plate; a jacket having a side plate and a bottom plate and firmly fixed to the top plate; a refrigerant inflow port through which a refrigerant flows into a space surrounded by the top plate and jacket; a refrigerant outflow port through which the refrigerant flows out from the space; a plurality of fins firmly fixed to the top plate and disposed separately on each of the left and right relative to a main refrigerant path in the jacket to be inclined toward the inflow side of the main refrigerant path; heat transfer pins disposed on the top plate on the refrigerant inflow sides of the fins; and a curved plate-like bimetal valve having one end connected to each respective heat transfer pin and another free end.