PURPOSE: To adapt an engine automatic stopping/starting device to an automatic transmission vehicle by composing automatic stopping conditions of an engine speed, a car speed, and presence/absence of a stopping allowance signal, and automatic stopping conditions of the engine speed, a shift lever position, and presence/absence of an accelerator idling condition.

CONSTITUTION: Automatic stopping conditions are composed of SP1 that en gine speed shows an idling state, SP2 that car speed is substantially zero, and SP3 that a stopping allowance signal is generated (ON) from a transmission control unit when a detected shift lever position is neutral. When all the conditions are effected, an engine is automatically stopped through a gate G2 indicating an OR condition and a gate G1 indicating an AND condition. An automatic starting conditions are composed of that an engine speed is zero, the shift lever is at a neutral position, and the detected accelerator condition is an idling condition. When the all conditions are effected, automatic starting is performed through gates indicating AND and OR conditions.