In a webbing take-up device, in a case in which the acceleration with which a webbing is pulled out from a spool, which is based on the radius of the webbing taken up on the spool and the angular acceleration of rotation of the spool in the pull-out direction that are detected by an angle-of-rotation sensor, is equal to or greater than a predetermined acceleration, a lock mechanism locks the rotation of the spool in the pull-out direction. For this reason, the rotation of the spool can be locked on based on the acceleration with which the webbing is pulled out from the spool.