A differential pressure valve simplified in construction includes a piston integrally formed with a main valve element and arranged on the upstream side of a main valve to define a chamber for introducing refrigerant from an inlet port. The piston has an orifice and a refrigerant passage for communicating with a chamber on a back surface side of the piston. The chamber is configured such that it can be connected, via a refrigerant passage and a pilot valve element, to a chamber on the downstream side of the main valve, which communicates with an outlet port.