To provide a relief valve which incorporates a proportional solenoid, and has a structure of suppressing chattering even if air bubbles are generated in an oil passage on a downstream side.

The relief valve 10 includes a damper chamber 40 communicating with an oil passage on an upstream side so as to suppress the vibration of a valve element 20 by the viscous resistance of oil flowing into the damper chamber 40. The damper chamber 40 and upstream side communication passages 38a and 38b communicate with each other by an orifice formed between circumferential side surfaces of a small-diameter part 22, a medium-diameter part 23, a small-diameter part 24, and a medium-diameter part 25, and an inner circumferential surface of a small diameter part 33 of a sleeve 32. Therefore, it can be prevented that, when the air bubbles are generated in the oil passage at the downstream side, oil rapidly flows to the oil passage with the air bubbles like the oil crushes the air bubbles, thus resulting in the insufficient inflow of the oil to the damper chamber as in a conventional technology in which the oil passage on the downstream side and the damper chamber communicate with each other.