To provide a seat belt device capable of detecting the rotating condition of a bobbin with high accuracy even during pulling out a webbing.

The seat belt device 100 includes the bobbin 106 for winding the webbing, an approximately disc-shaped magnetic disc 126 connected to a rotating shaft 110 of the bobbin 106, and contactless Hall elements 130A, 130B disposed outside the periphery of the magnetic disc 126 for detecting the rotating condition of the magnetic disc 126. The Hall elements 130A, 130B are disposed in the radial direction of the magnetic disc 126, approximately perpendicular to a direction 157 of pulling the webbing out of the bobbin 106.