A straddled vehicle comprising: a single-cylinder engine including a piston and a crankshaft, the piston is provided in a cylinder and moveable to and fro by combustion of a mixed gas containing air and a fuel, the crankshaft is configured to be rotated along with the to-and-fro movement of the piston; a drive wheel configured to receive a rotational force outputted from the single-cylinder engine via the crankshaft and to drive the straddled vehicle; an acceleration command part configured to instruct that the straddled vehicle be accelerated in accordance with an operation thereon; a throttle valve arranged in an intake passage (Ip) connecting with the single-cylinder engine, and configured to be opened to a degree that is based on the amount of operation on the acceleration command part so that an amount of the air is supplied to the single-cylinder engine, the amount corresponding to the degree of opening; a permanent magnet type motor including a rotor and a permanent magnet, the rotor is connected directly or indirectly to the crankshaft so as to be rotatable in response to rotation of the crankshaft, the permanent magnet provided to the rotor; a battery; an inverter including a plurality of switching parts (611 to 616) configured to control a current flowing between the battery and the permanent magnet type motor; and a control device configured to control the plurality of switching parts (611 to 616) so as to assist a piston operation by directing the permanent magnet type motor to apply a force to the piston via the crankshaft such that the force cooperates with a force generated by combustion in the single-cylinder engine to move the piston to and fro, the control is triggered by the amount of operation on the acceleration command part being increased when logical OR of a condition regarding the amount of operation on the acceleration command part and a condition regarding the rate of increase in the amount of operation on the acceleration command part is satisfied irrespective of how long a state of the increase in the amount of operation on the acceleration command part continues under a state where the throttle valve is not in a full-open state and the piston is moved to and fro by combustion of the mixed gas. a single-cylinder engine including a piston and a crankshaft, the piston is provided in a cylinder and moveable to and fro by combustion of a mixed gas containing air and a fuel, the crankshaft is configured to be rotated along with the to-and-fro movement of the piston; a drive wheel configured to receive a rotational force outputted from the single-cylinder engine via the crankshaft and to drive the straddled vehicle; an acceleration command part configured to instruct that the straddled vehicle be accelerated in accordance with an operation thereon; a throttle valve arranged in an intake passage (Ip) connecting with the single-cylinder engine, and configured to be opened to a degree that is based on the amount of operation on the acceleration command part so that an amount of the air is supplied to the single-cylinder engine, the amount corresponding to the degree of opening; a permanent magnet type motor including a rotor and a permanent magnet, the rotor is connected directly or indirectly to the crankshaft so as to be rotatable in response to rotation of the crankshaft, the permanent magnet provided to the rotor; a battery; an inverter including a plurality of switching parts (611 to 616) configured to control a current flowing between the battery and the permanent magnet type motor; and a control device configured to control the plurality of switching parts (611 to 616) so as to assist a piston operation by directing the permanent magnet type motor to apply a force to the piston via the crankshaft such that the force cooperates with a force generated by combustion in the single-cylinder engine to move the piston to and fro, the control is triggered by the amount of operation on the acceleration command part being increased when logical OR of a condition regarding the amount of operation on the acceleration command part and a condition regarding the rate of increase in the amount of operation on the acceleration command part is satisfied irrespective of how long a state of the increase in the amount of operation on the acceleration command part continues under a state where the throttle valve is not in a full-open state and the piston is moved to and fro by combustion of the mixed gas.