A passenger protection system includes: a sensor outputting a detection digital data corresponding to collision; a passenger protection device; and an ECU. The sensor outputs a bit sequence providing an important bit group. A memory stores the data and the sequence doubly for storing first and second detection digital data and first and second bit sequences. The ECU determines based on the first or second data whether it is necessary to protect the passenger when the first data is equal to the second data. When the first data is different from the second data, and the first sequence is equal to the second sequence, the ECU replaces the important bit group in the first or second data with the first or second sequence, and determines based on the first or second data after replacement.