Abstract: A pressure-relief and cutoff device for an air compressor has a body, a link rod, a cutoff assembly and a bleed assembly. The body has a first adapting tube connecting to a reservoir, a second adapting tube connecting to a pump and the reservoir and a bottom opening. The link rod is mounted movably in the body. The cutoff assembly has a diaphragm attached to the link rod, an actuating rod and two terminals electrically connecting to the motor. The terminals respectively have a resilient contact and a stationary contact. The bleed assembly has a stopper attached to the link rod and selectively sealing the bottom opening of the body. When the air pressure in the reservoir is too great, the air bends the diaphragm to push the resilient contact to disconnect from the contact to stop the motor. The pump stops operating immediately to prevent damage by backflow.