A webbing take-up device comprising a spool and a locking unit having a locking unit main body having a rotational acceleration detecting unit, wherein the rotational acceleration detecting unit comprises a second rotating body; a rotation transmission member provided at the second rotating body; an inertial mass body having a pressing portion and provided at the second rotating body; a biasing means provided at the second rotating body; and a retaining portion provided at the second rotating body to pinch the rotation transmission member together with the inertial mass body biased by the biasing means, thereby retaining the rotation transmission member in a state in which the rotation transmission member does not engage with the first rotating body, and to release retention of the rotation transmission member when relative rotation is produced between the second rotating body and the inertial mass body.