To provide a hydrogen generator capable of easily discriminating whether a hydrogen generating material container has been unused or used, and a fuel cell system using this.

The hydrogen generator is equipped with a hydrogen generating material container 1 which holds a hydrogen generating material 2 which generates hydrogen by an exothermic reaction with water, a water supplying part 3 which supplies water to the inside of the hydrogen generating material container 1, and a temperature detection part 5 which is installed at the external surface of the hydrogen generating material container 1 and detects the elevation of a surface temperature of the hydrogen generating material container 1 using an irreversible material which detects temperature change and yields an irreversible change of state. On the temperature detection part 5, an irreversible material which is irreversibly discolored when temperature change yielded by an exothermic reaction of the hydrogen generating material 2 and water is detected is applied.