To provide the wear monitor of a gas insulated circuit breaker in which wear of components in the gas insulated circuit breaker can be judged conveniently and accurately even when decomposition gas is adsorbed by adsorbent.

Adsorbent 11 for adsorbing a specified amount of the decomposition gas of insulating gas is arranged in an enclosed container 2 encapsulating the insulating gas of the gas insulated circuit breaker 1. A wear judging unit 15 judges that a component of the gas insulated circuit breaker 1 has worn and must be replaced if the concentration of decomposition gas is not lower than an allowable level L0 when a predetermined time T1 has elapsed after the current is interrupted.