A quick-action locking device for an electric power tool including a locking spindle (4) axially displaceable in the hollow spindle (2) of the electrical power tool between a working tool locking position and a working tool exchange position, and a locking lever (6) provided at the end of the locking spindle remote from the working tool and having a slider cooperating with the locking spindle (4) for displacing the same, upon a pivotal movement of the locking lever (6), to its tool exchange position, with the slider (8) having a contact region engageable with a contact surface provided at the end of the locking spindle (4) remote from the working tool (3), and with the contact surface of the locking spindle (4) having an extent, in a pivotal direction of the locking lever (6), corresponding to at least the radial distance (a) of the contact region from the pivot axis (9) of the lever multiplied, in the locking position of the locking lever (6), by a sin (null) of an angle formed by a line, which defines the radial distance (a), with a longitudinal axis of the locking spindle (4).