PURPOSE: To facilitate the assembling of a rail by moving the other side part of a moving base to the right and left to one part of straight rails via a slider, in case of the parallelism of a pair of straight rails of a linearly advancing guide unit being not secured.

CONSTITUTION: A 1st straight rail 1 and 2nd straight rail 2 are provided along a reference face 3a which is provided with its projection on a support base 3 and a vertical support part 2a and horizontal guide part 2b are formed on the 2nd straight rail 2. One side part of a moving base 8 guided by these straight rails 1, 2 is slidably supported along the rail 1 in the state of the movement in the right and left directions being regulated by the 1st straight rail 1 via a 1st slider 5. Also, the other end part of the moving base 8 is regulated at its movement in the vertical direction by the horizontal guide part 2b of the 2nd straight rail 2 via 2nd slider 7 and also supported slidably along the rail in the state of being made movably in the horizontal direction.