An electronic control unit includes a seat temperature calculating unit, a supply amount control unit, and a concentration acquiring unit. The seat temperature calculating unit calculates a simulated temperature of an exhaust valve seat. When the simulated temperature of the exhaust valve seat becomes equal to or higher than a threshold temperature, the supply amount control unit starts fuel increase control of increasing a lower limit value of an amount of fuel to be supplied into a cylinder to a larger value than that before the simulated temperature becomes equal to or higher than the threshold temperature. The concentration acquiring unit acquires an ethanol concentration of the fuel. In the fuel increase control, the supply amount control unit makes the amount of increase in the lower limit value larger as the ethanol concentration of the fuel acquired by the concentration acquiring unit is higher.