An object is to optimize a back pressure pressing an orbiting scroll against a fixed scroll in a scroll compressor to which an injection cycle is applied. A back pressure control valve (400) adjusting back pressure (Pm) in a back pressure chamber (H4), adjusts the opening degree of a first valve body (424) increasing and decreasing the flow rate of lubricant which has been separated from gaseous refrigerant compressed in a compression chamber and is supplied to the back pressure chamber (H4), in accordance with suction pressure (Ps) in a suction chamber (H1), discharge pressure (Pd) in a discharge chamber (H2), and injection pressure (Pinj). Then, the back pressure control valve (400) increases and decreases the lubricant flow rate in accordance with injection pressure (Pinj) as well as suction pressure (Ps) and discharge pressure (Pd), to adjust back pressure to target back pressure varying in accordance with injection pressure (Pinj).