To provide a purging timer capable of eliminating useless time on device starting or restarting.

The purging timer includes: a first timer connected to a power source disposed in a pressure resistant explosion-proof container; a first relay for turning ON/OFF the power source according to an output signal from the first timer; a first heat generation device disposed in a first inner pressure explosion-proof container to receive power when the first relay is ON; a second pressure resistant explosion-proof container disposed in the first inner pressure explosion-proof container; power supply unit disposed in the second pressure resistant explosion-proof container; a second timer connected to the power generation unit; a second relay disposed in the first inner pressure explosion-proof container to turn ON/OFF the power source according to an output signal from the second timer; a second heat generation device disposed in a second inner pressure explosion-proof container to receive power when the second relay is ON; and a monitoring unit for starting or stopping counting of the first and second timers according to a normal or an abnormal purging state in the first and second inner pressure exposion-proof containers.