A waste heat recovery apparatus includes a Rankine cycle (20) which includes a heater (22) for heating an operation fluid by waste heat from a heat-generating device (10), an expansion unit (23) for converting energy of expansion of the operation fluid flowing out from the heater (22) into mechanical energy, and a condenser (24) for condensing and liquefying the expanded operation fluid, a temperature detector (206) for detecting the temperature of the operation fluid on the inlet side of the expansion unit (23), a pressure detector (207) for detecting inlet-side pressure (Pex_in) of the expansion unit (23), a pressure detector (208) for detecting outlet-side pressure (Pex_out) of the expansion unit (23), and control units (30, 32). The control units control a command rotational speed (N_id) of the expansion unit (23) based on superheated degree information (SH) at the inlet of the expansion unit obtained from the operation fluid temperature and the inlet-side pressure, and pressure information (P) in which the outlet-side pressure (Pex_out) is considered.