Fluid machine operable in both pump mode and motor mode and waste heat recovering system having the same

A check valve is provided to each discharge port (105, 409), which communicates between a corresponding working chamber (103, V) and a high pressure chamber (104, 407) in an integrated compressor/expander apparatus (10). A valve mechanism (107, 411), which is opened in a motor mode, is provided to communicate between the working chamber (103, V) and the high pressure chamber (104, 407).