The occupant protection device (air bag ECU 1) of the invention is composed of an input signal acquisition unit 11 for acquiring acceleration signals or angular velocity signals from sensors installed in a vehicle, a digital signal processing unit 12 for generating an output signal in a time series of the acceleration signals or angular velocity signals composed of consecutive first, second and third intervals by changing a multiplication factor of the second interval in comparison with the first and third intervals, a status determination unit 13 for determining a collision or rollover of the vehicle based on the output signal, and an air bag actuation circuit 14 for igniting a squib 32.