Abstract: A device for actuating a timepiece mechanism, in particular a chronograph mechanism, this timepiece including a fitting ring (12) having an opening (14) for accommodating a movement (16), an independent push-button (4a, 4b) sliding along a first direction (D1), a piston (18a, 18b) sliding along a second direction (D2, D3) in the fitting ring (12), said piston (18a, 18b) being intended to co-operate with a component of the movement and a push transmission element to transmit a push of said pushbutton (4a, 4b) to said piston (18a, 18b), characterized in that the push transmission element includes a rigid actuation lever (22a, 22b) articulated at one point (P) on the fitting ring (12) and in the plane thereof.