An output state detecting apparatus is arranged to detect a reaction torque of a motor and detect an output state of an internal-combustion engine from the reaction torque. The apparatus comprises an internal-combustion engine, a generator driven by the internal-combustion engine to generate electric power, torque detecting means for detecting a reaction torque of this generator, and output state detecting means for detecting an output state of the internal-combustion engine. The output state detecting means detects the output state of the internal-combustion engine, based on the reaction torque of the motor detected by the torque detecting means.