An occupant protection device includes a knee air bag. The knee air bag is configured to be deployed rearwardly from a front of right and left knees of an occupant seated in a seat of a vehicle towards the knees to press the knees from the front. The knee air bag includes at least either one of a right side inclined surface and a left side inclined surface. The right side inclined surface is configured to come in contact, from a right side, with the right knee of the occupant seated in the seat and the left side inclined surface is configured to come in contact with the left knee of the occupant from a left side.