A coolant tank includes: a tank main body configured to store a coolant discharged from a processing machine; a vortex flow generator that creates a vortex flow of the coolant in the tank main body; and a float configured to float on a liquid surface of the coolant stored in the tank main body. An outer peripheral portion of the float has a shape conforming to a shape of an inner peripheral wall surface of the tank main body and forming a gap between the outer peripheral portion and the inner peripheral wall surface.