A spark ignition type engine adjusts a base lower limit value of a valve opening degree of an ISC valve to avoid excessive engine rotation that may occur when an increase correction by atmospheric pressure is performed. When a detected engine temperature becomes lower, the base lower limit value of the ISC valve opening degree is increased to the fully open side, and the base lower limit value is corrected to increase to the fully open side with an increase correction value on the basis of a detected atmospheric pressure in an engine middle-high temperature range where the engine temperature exceeds a predetermined value, and the increase correction value is increased to the fully open side as the detected atmospheric pressure becomes lower, and the increase correction is prohibited in an engine low temperature range where the engine temperature is equal to or lower than the predetermined value.