When a second member of a power plant is in a first position with respect to a first member, a first communication port communicates with a fluid pressure supply source and second and third communication ports communicate with first and second pressure chambers of a fluid pressure motor. The second and third communication ports are shut off from a fourth communication port connected to a reservoir. Different positions of the second member result different communication and shut off relationships among the first to fourth ports. The first to fourth communication ports are provided in a plurality of communication port groups each formed by the first to fourth communication ports.