PURPOSE: To properly control air bag operation timing based on car body acceleration and a relative speed, relating to an air bag operation control device by which an air bag is inflated for relaxing impact of an occupant at collision time of a vehicle.

CONSTITUTION: A relative speed Vx is read to calculate a correction threshold value Cx based on the Vx (step 101, 102). This correction threshold value Cx is compared with an acceleration mean value (accumulated value) Vi for a level in a step 107. An air bag operation threshold value is calculated to a value smaller in accordance with increasing the relative speed. In this way, air bag operation timing is controlled in accordance with the relative speed Vx.