A reciprocating tool includes a motor, a crank, a connecting rod, a rod, a tool bit, and a counter weight. The tool bit is mounted such that the action portion is positioned on a side opposite to a side with the rod central axis or the extended line of the rod central axis viewing from the rotational center of the crank. The first eccentric shaft and the second eccentric shaft are disposed such that at a position where the first eccentric shaft causes the rod to reach top dead center (TDC), the second eccentric shaft causes the counter weight to reach bottom dead center (BDC) or a point before the BDC, and at a position where the first eccentric shaft causes the rod to reach the BDC, the second eccentric shaft causes the counter weight to reach a point before the TDC.

A mass-balancing arrangement comprises an adjustably pre-loaded spring member (14); a pivotably mounted lever (16; 31) for compensating different inertial forces in combination with the spring member (14); a first drawing member (24) connecting a movable mass to the lever (16); a second drawing member (17) connecting the spring member (14) to the lever (16); and a first roller (15) for deflecting the first drawing member (24). The lever (16; 31) has an upper lever arm (19; 32) and a lower lever arm (20; 33), one being sector-shaped and the other cam-shaped. The upper lever arm is connected to the movable mass through the first drawing member (24), and the lower lever arm is connected to the spring (14) through the second drawing member (24). Two torques produced at the upper and lower lever arms are kept balanced. The balanced mass may be an object carriage of a microtome.