An ion exchanger includes a case that is provided with an opening, an intake port, and a discharge port. The opening opens upward in the case. Coolant is drawn into the lower portion of the case through the intake port and discharged through the discharge port. An ion exchanging resin member and a cap are provided in the case. The ion exchanging resin member removes ions from the coolant. The cap is detachably attached to the case and closes the opening of the case. The ion exchanger further includes a tube member that is arranged to extend vertically in the case. The lower end aperture of the tube member is connected to the discharge port of the case. The upper end aperture of the tube member faces the inner top surface of the lid portion of the cap.