The invention relates to a chronographic timepiece and a chronograph mechanism (7) thereof including an elapsed time indicator member (17), a reset control member (21), and a reset device (25) for the indicator member, which includes a hammer (61), mounted in translation between an inactive position, where the hammer (61) is moved away from heart-pieces (55, 57, 59) that are connected to the indicator member (17), and an active position where stop members (54, 56, 58) of the hammer exert a reset force against the heart-pieces. The hammer (61) includes two studs (64, 66) mounted so as to slide in holes (100, 102) such that the movement vectors (L, K) of the studs (64, 66) between the positions are collinear and not aligned.