A seat belt device allowing easy connection of a lap anchor fixed to one end of a seat belt relative to a vehicle body or the like even when a seat weight sensor is installed below a vehicle seat. The seat weight sensor and the vehicle seat are fixed to a vehicle body floor. A hitch member is attached to the seat weight sensor via a mounting bracket by a bolt. A lap anchor is fixed to one end of a seat belt. By locking the lap anchor to the hitch member, the seat belt is connected to the seat weight sensor. In this manner, the seat belt can be easily connected to the vehicle body just by locking the lap anchor to the hitch member.