A passenger protection apparatus is provided with a plurality of squibs (activating elements). Transistors are respectively connected in series to these squibs. By switching on these transistors at predetermined differing timing, first monitor currents are conducted via current-controlling resistors to the respective squibs. First monitor currents can be independently conducted to the respective squibs with this structure. For this reason, the voltage levels generated at the squibs by the first monitor currents can be enlarged. Resistance values of the respective squibs can be calculated with high accuracy from these voltage values.