PURPOSE: To properly correct the shift judgement always regardless of secular change in the engine.

CONSTITUTION: At S31 thru S36, judgement is made whether an engine is with no load and in a predetermined idling condition as a substantially constant operating condition, and S37 determines the difference ΔQNIDL of the preset at-idling suction air amount KQIDL from the actual suction air amount Qm is determined in the idling condition, and S41 updates the secular change correction value KGDLQN on the basis of the determined difference ΔQNIDL. The updated KGDLQN is added to the requisite suction air amount determined on the basis of the engine revolving speed and the degree of throttle valve opening, and the sum is divided with the actual suction air amount Qm. and thereby the correction factor for correcting shift judgement is calculated.