Disclosed is a passenger protection device provided with a side curtain airbag which expands in the form of a curtain, along the inner surface of a side portion of a vehicle. A side curtain airbag (31) is comprised of a gas introduction chamber (40) which introduces gas; and lower expansion portions (51, 52) which are expanded in the lower portion of the gas introduction chamber by the gas introduced from the gas introduction chamber. The gas introduction chamber has a plurality of large upper expansion portions (42, 43, 44) which are arranged in the longitudinal direction of a vehicle, so as to be respectively positioned in a plurality of pillars (15, 16, 17). The large upper expansion portions expand more widely than small expansion portions (45, 46), i.e., other portions of the gas introduction chamber, in the width direction of a vehicle.