A method of assembling a rotary compressor comprising a set of two compressing units (12S, 12T) each of which includes: - an annular cylinder (121S, 121T) including a flared portion (122S, 122T) to provide an inlet hole (135S, 135T) and a vane groove (128S, 128T); - a lower end plate and an upper end plate or a partition to seal an end of the cylinder (121S, 121T); - an annular piston (125S, 125T) held by an eccentric portion (152S, 152T) of a rotation shaft rotationally driven by a motor, the annular piston (125S, 125T) revolving along a cylinder inner wall (123S, 123T) in the cylinder (121S, 121T), an operation chamber (130S, 130T) being formed between the cylinder inner wall (123S, 123T) and the annular piston (125S, 125T); - a vane (127S, 127T) protruding from the vane groove (128S, 128T) provided to the flared portion (122S, 122T) of the cylinder (121S, 121T) into the operation chamber (130S, 130T) and coming in contact with the annular piston (125S, 125T) to partition the operation chamber (130S, 130T) into an inlet chamber (131S, 131T) and a compression chamber (133S, 133T); - a spring (126S, 126T) and a spring hole (124S, 124T) formed in a back of the vane groove (128S, 128T); and - a pin hole (310S, 310T) located on an outer circumferential side of an end of the vane groove (128S, 128T) provided to the flared portion (122S, 122T) of the cylinder (121S, 121T) and crossing the spring hole (124S, 124T), - the method comprising inserting the spring (126S, 126T) into the spring hole (124S, 124T) to press a back of the vane (127S, 127T) in each of the compressing units, characterized in that the method further comprises inserting a spring holder pin including a handle through the pin holes (310S, 310T) while holding the handle to prevent the springs (126S, 126T) pushed into the spring holes (124S, 124T) from coming off the first spring hole and the second spring hole, respectively, when the set of two compressing units (12S, 12T) is installed in a compressor housing. - an annular cylinder (121S, 121T) including a flared portion (122S, 122T) to provide an inlet hole (135S, 135T) and a vane groove (128S, 128T); - a lower end plate and an upper end plate or a partition to seal an end of the cylinder (121S, 121T); - an annular piston (125S, 125T) held by an eccentric portion (152S, 152T) of a rotation shaft rotationally driven by a motor, the annular piston (125S, 125T) revolving along a cylinder inner wall (123S, 123T) in the cylinder (121S, 121T), an operation chamber (130S, 130T) being formed between the cylinder inner wall (123S, 123T) and the annular piston (125S, 125T); - a vane (127S, 127T) protruding from the vane groove (128S, 128T) provided to the flared portion (122S, 122T) of the cylinder (121S, 121T) into the operation chamber (130S, 130T) and coming in contact with the annular piston (125S, 125T) to partition the operation chamber (130S, 130T) into an inlet chamber (131S, 131T) and a compression chamber (133S, 133T); - a spring (126S, 126T) and a spring hole (124S, 124T) formed in a back of the vane groove (128S, 128T); and - a pin hole (310S, 310T) located on an outer circumferential side of an end of the vane groove (128S, 128T) provided to the flared portion (122S, 122T) of the cylinder (121S, 121T) and crossing the spring hole (124S, 124T), - the method comprising inserting the spring (126S, 126T) into the spring hole (124S, 124T) to press a back of the vane (127S, 127T) in each of the compressing units, characterized in that the method further comprises inserting a spring holder pin including a handle through the pin holes (310S, 310T) while holding the handle to prevent the springs (126S, 126T) pushed into the spring holes (124S, 124T) from coming off the first spring hole and the second spring hole, respectively, when the set of two compressing units (12S, 12T) is installed in a compressor housing.