A first table (1) slidable leftwards and rightwards of a gear finishing machine and a second table (2) slidable forwards and rearwards of the machine are disposed in an overlapped relationship such that one of the tables is mounted on the top of the other table. Of these tables, the upper table is guided by a horizontal guide member (3) which is adapted to be rotated to any desired angular position and to be clamped at such position. A feed motor (5) drives the first table to slide.For sliding the table assembly along a diagonal direction, the angular position of the guide member is adjusted so that it extends along such direction.A horizontal stability of the table assembly is secured without employing a conventional parallel link mechanism. The table assembly is driven to slide so as to pass the center of machine so that an accuracy of gear finishing is assured.