An ion exchanger configured to remove an impurity ion of a coolant for cooling a fuel cell, the ion exchanger includes an inflow portion having an inflow path where the coolant enters, a discharge portion having a discharge path for discharging the coolant, an outer casing having an upstream end where the inflow portion is provided and a downstream end where the discharge portion is provided, an inner casing housed inside the outer casing, an outer path formed between the inner casing and the outer casing to cause the inflow path and the discharge path to communicate with each other, and an inner path that is formed inside the inner casing to cause the inflow path and the discharge path to communicate with each other and is configured to enclose an ion exchange resin capable of removing an impurity ion of the coolant. The inner casing has a through-hole that causes the inner path and the outer path to communicate with each other.