To prevent any bending stress from being imposed on an output shaft being equipped with a driving pulley, from a V-belt even if rotating a bracket for adjusting the tension of this V-belt in the case where two compressors are attached to both sides of an engine via the bracket, and the V-belt is stretched across a driving pulley of the engine and a driven pulley of the compressor.

A bracket 17 equipped with a compressor 2 and a bracket 18 equipped with another compressor 3 are made rotatably in the same direction in use of a guide hole 26 fitted with a rod 14 or 16 as an adjusting mechanism, with a rod 13 or 15 as the rotational fulcrum, whereby respective rotational ratios of both these brackets 17 and 18 are equalized. With this constitution, an axis A of a driving pulley 5, an axis B of a driven pulley 22 and an axis C of another driven pulley 23 are held on the same line.