The activating device (20) for an occupant protection device includes a first deceleration detecting means (22) for detecting a first deceleration G in vehicle front/rear direction and an activation judging means (37) for judging whether the activation of the occupant protection device is necessary or not by comparing the first deceleration G detected by the first deceleration detecting means (22) with a first threshold value. The device further includes a second deceleration detecting means (24, 26) for detecting a deceleration LG, RG at a position further front side of the vehicle than the position detecting the first deceleration, a collision condition detecting means (35) for detecting a vehicle collision condition based on a second threshold value by the deceleration LG and RG and a first threshold changing means (36) for changing the first threshold value of an activation judging means (37) based on the detected result of the collision condition detecting means (35).