A Rankine-cycle power-generating apparatus (100; 200) comprising: a Rankine-cycle device including: an expander configured to convert expansion energy of a working fluid into mechanical energy, a bypass flow channel configured to bypass the expander, an opening/closing device configured to open/close the bypass flow channel whose degree of opening is adjustable to any of a fully opened state, a fully closed state, and an intermediate degree of opening between the fully opened state and the fully closed state, and a power generator that is linked to the expander; and a control device (2; 202) including: a converter configured to convert alternating-current electric power generated by the power generator into direct-current electric power, and an inverter that is connected to the converter via a direct-current electric power line and that is configured to convert the direct-current electric power into alternating-current electric power and feeding the alternating-current electric power to a commercial system, characterized in that the control device (2; 202) includes an electric power absorber configured to absorb part of or all of the direct-current electric power, wherein the control device (2; 202) is configured to: a) adjust the degree of opening of the opening/closing device so that the direct-current electric power absorbed by the electric power absorber approaches a first electric power (P1, P1'), or b) increase the degree of opening of the opening/closing device to a predetermined intermediate degree of opening so that the direct-current electric power absorbed by the electric power absorber falls within a predetermined range. a Rankine-cycle device including: an expander configured to convert expansion energy of a working fluid into mechanical energy, a bypass flow channel configured to bypass the expander, an opening/closing device configured to open/close the bypass flow channel whose degree of opening is adjustable to any of a fully opened state, a fully closed state, and an intermediate degree of opening between the fully opened state and the fully closed state, and a power generator that is linked to the expander; and an expander configured to convert expansion energy of a working fluid into mechanical energy, a bypass flow channel configured to bypass the expander, an opening/closing device configured to open/close the bypass flow channel whose degree of opening is adjustable to any of a fully opened state, a fully closed state, and an intermediate degree of opening between the fully opened state and the fully closed state, and a power generator that is linked to the expander; and a control device (2; 202) including: a converter configured to convert alternating-current electric power generated by the power generator into direct-current electric power, and an inverter that is connected to the converter via a direct-current electric power line and that is configured to convert the direct-current electric power into alternating-current electric power and feeding the alternating-current electric power to a commercial system, characterized in that the control device (2; 202) includes an electric power absorber configured to absorb part of or all of the direct-current electric power, a converter configured to convert alternating-current electric power generated by the power generator into direct-current electric power, and an inverter that is connected to the converter via a direct-current electric power line and that is configured to convert the direct-current electric power into alternating-current electric power and feeding the alternating-current electric power to a commercial system, wherein the control device (2; 202) is configured to: a) adjust the degree of opening of the opening/closing device so that the direct-current electric power absorbed by the electric power absorber approaches a first electric power (P1, P1'), or b) increase the degree of opening of the opening/closing device to a predetermined intermediate degree of opening so that the direct-current electric power absorbed by the electric power absorber falls within a predetermined range. a) adjust the degree of opening of the opening/closing device so that the direct-current electric power absorbed by the electric power absorber approaches a first electric power (P1, P1'), or b) increase the degree of opening of the opening/closing device to a predetermined intermediate degree of opening so that the direct-current electric power absorbed by the electric power absorber falls within a predetermined range.