A retractor 100 for a seat belt to be mounted within a seat back of a reclining type seat. The retractor 100 comprises a winding shaft 4 for winding a webbing 90 therearound, a lock element of an emergency lock mechanism 300 for locking the rotation of the winding shaft 4 in the webbing drawn-out direction thereof, and a vehicle body acceleration sensor 32 for detecting a given vehicle body acceleration to thereby actuate the lock element. The lock element of the emergency lock mechanism 300 is structured such that, while the seat belt is not in use, if the seat back is set within the range from the most forwardly inclined position of the seat back to the the most backwardly inclined position of the seat back, a locking wall 41c of a rotation control disk 41 is contactable with a securing piece 15d of an engaging member 15 to thereby prevent the engaging member 15 from moving in a direction where it can be engaged with a latch cup 13.