A method for controlling an engine unit for a straddled vehicle, the engine unit comprises an engine having a crankshaft and an electric component (18, 19); a rotating electrical machine power-transmittably coupled to the crankshaft and configured to be used in common as a starter motor for rotating the crankshaft and as a generator for generating electric power by a rotating force of the crankshaft; a power supply line (71, 72) that is connected to a battery, and that is connected to the electric component (18, 19); an inverter including a plurality of switching devices (611 to 616) configured to control a current flowing between the power supply line (71, 72) and the rotating electrical machine; the method comprises: executing a power generation control (S8, S9, S22) of controlling the plurality of switching devices (611 to 616) of the inverter to make the rotating electrical machine perform power generation, and executing, when the crankshaft is rotated by a manual starter that applies an external force other than a rotating force of the rotating electrical machine with the engine being in a stop state, the power generation control in a start power generation region in which a rotational speed of the crankshaft is not more than a cranking rotational speed in rotation by the rotating electrical machine, wherein the power generation control includes a vector control (S9, S22) of controlling the plurality of switching devices (611 to 616) included in the inverter by a vector control method to boost the voltage generated by the rotating electrical machine and lead out the thus boosted voltage, to the power supply line (71, 72), and the power generation control includes a phase control of controlling the plurality of switching devices (611 to 616) included in the inverter by a phase control method, wherein the vector control is performed in a region of the engine speed up to a control method changing threshold and the phase control is performed in a region exceeding the control method changing threshold, and switching from the vector control to the phase control in response to the rotational speed of the crankshaft reaching or exceeding the control method changing threshold that is greater than the cranking rotational speed. executing a power generation control (S8, S9, S22) of controlling the plurality of switching devices (611 to 616) of the inverter to make the rotating electrical machine perform power generation, and executing, when the crankshaft is rotated by a manual starter that applies an external force other than a rotating force of the rotating electrical machine with the engine being in a stop state, the power generation control in a start power generation region in which a rotational speed of the crankshaft is not more than a cranking rotational speed in rotation by the rotating electrical machine, wherein the power generation control includes a vector control (S9, S22) of controlling the plurality of switching devices (611 to 616) included in the inverter by a vector control method to boost the voltage generated by the rotating electrical machine and lead out the thus boosted voltage, to the power supply line (71, 72), and the power generation control includes a phase control of controlling the plurality of switching devices (611 to 616) included in the inverter by a phase control method, wherein the vector control is performed in a region of the engine speed up to a control method changing threshold and the phase control is performed in a region exceeding the control method changing threshold, and switching from the vector control to the phase control in response to the rotational speed of the crankshaft reaching or exceeding the control method changing threshold that is greater than the cranking rotational speed.