An occupant protection device comprising: a vehicle seat including a seat cushion and a seatback; a vehicle seatbelt device including a three-point seatbelt configured to restrain an occupant in the vehicle seat, the three-point seatbelt comprising a shoulder belt; and a vehicle side airbag device installed at a side section on a vehicle width direction outer side of the seatback, the vehicle side airbag device comprising: an inflator configured to generate gas in a vehicle side-on collision; a side airbag including a waist chamber configured to inflate and deploy from a lower portion of the side section toward a side of a waist of the occupant on receiving a supply of gas from the inflator, and a head chamber configured to inflate and deploy from an upper face (16A1) side of the side section toward a side of a head of the occupant on receiving a supply of gas from the inflator, the side airbag being housed inside the side section in a folded state; and a duct that extends along a vertical direction of the side airbag inside the side airbag, and is configured to guide gas from the inflator into the waist chamber and into the head chamber; characterized in that, in the housed state of the side airbag, a location including the head chamber extends from a shoulder part of the seatback toward a headrest and the side airbag bends at the height of the shoulder part towards a vehicle width inner side, so that the head chamber is configured to inflate and deploy further towards the vehicle width inner side than the shoulder belt of the seatbelt. a vehicle seat including a seat cushion and a seatback; a vehicle seatbelt device including a three-point seatbelt configured to restrain an occupant in the vehicle seat, the three-point seatbelt comprising a shoulder belt; and a vehicle side airbag device installed at a side section on a vehicle width direction outer side of the seatback, the vehicle side airbag device comprising: an inflator configured to generate gas in a vehicle side-on collision; a side airbag including a waist chamber configured to inflate and deploy from a lower portion of the side section toward a side of a waist of the occupant on receiving a supply of gas from the inflator, and a head chamber configured to inflate and deploy from an upper face (16A1) side of the side section toward a side of a head of the occupant on receiving a supply of gas from the inflator, the side airbag being housed inside the side section in a folded state; and a duct that extends along a vertical direction of the side airbag inside the side airbag, and is configured to guide gas from the inflator into the waist chamber and into the head chamber; characterized in that, in the housed state of the side airbag, a location including the head chamber extends from a shoulder part of the seatback toward a headrest and the side airbag bends at the height of the shoulder part towards a vehicle width inner side, so that the head chamber is configured to inflate and deploy further towards the vehicle width inner side than the shoulder belt of the seatbelt. an inflator configured to generate gas in a vehicle side-on collision; a side airbag including a waist chamber configured to inflate and deploy from a lower portion of the side section toward a side of a waist of the occupant on receiving a supply of gas from the inflator, and a head chamber configured to inflate and deploy from an upper face (16A1) side of the side section toward a side of a head of the occupant on receiving a supply of gas from the inflator, the side airbag being housed inside the side section in a folded state; and a duct that extends along a vertical direction of the side airbag inside the side airbag, and is configured to guide gas from the inflator into the waist chamber and into the head chamber; characterized in that, in the housed state of the side airbag, a location including the head chamber extends from a shoulder part of the seatback toward a headrest and the side airbag bends at the height of the shoulder part towards a vehicle width inner side, so that the head chamber is configured to inflate and deploy further towards the vehicle width inner side than the shoulder belt of the seatbelt.