Provided is an activation system for a passenger protection apparatus capable of detecting a collision acceleration accurately and in detail with a simple configuration for appropriately activating apparatus. A satellite sensor unit side converts a detection output from an electronic acceleration sensor into a digital collision acceleration data and sequentially it to a communication line at a predetermined cycle, while an air bag control unit side makes a decision on collision at a front portion of a vehicle on the basis of a central-portion acceleration detected by an acceleration sensor and the collision acceleration data received through the line for the activation of air bags. This configuration enables only the air bag control unit side to make a collision decision without making a collision decision in the satellite sensor unit side, which allows a simple and low-cost system.