The waste heat power generator (G) includes: an evaporator (1) configured to produce steam of a working medium; a power-generating device (2, 2a, 2b) configured to generate electric power while expanding the steam; a condenser (3) configured to condense the steam which has passed through the power-generating device (2, 2a, 2b); and a pump (5) configured to send the condensed working medium to the evaporator (1). A bottom portion (BT) of the power-generating device (2, 2a, 2b) is provided with a discharge port (8) configured to discharge the working medium liquefied inside the power-generating device (2, 2a, 2b), to the outside thereof. A discharge pipe (6) is provided in which one end thereof is connected to the discharge port (8) and the other end thereof is disposed in a channel for the working medium between the condenser (3) and the pump (5).