A method of calculating torque of a Lundell-type synchronous generator is disclosed in which only power generation output current and a rotational speed are input for calculation of the amount of electric power and the amount of losses for thereby enabling calculation of power generating torque, based on a sum of the amount of electric power and the amount of losses, which is generated as an output. The present method establishes formulae enabling calculation based on only output current and the rotational speed, enabling a minimal number of inputs to shorten a calculation time interval.