PURPOSE: To aim at keeping a comfortable ride in a cabin unimpaired, by setting up a coupling mechanism interposingly in a tilt cylinder providing a tilting motion for the cabin of cab-over engine cars, etc., while making the cylinder releasable in time of nonrequirement.

CONSTITUTION: A coupling mechanism consisting of a coupling ring 20, a coupling bracket 22, etc., is interposingly set up between a cabin 4 and a tilt cylinder 16, and this coupling mechanism is released as the cabin 4 requires no tilting motion. When the cabin 4 is tilted, a rod 19 is pressed out through the cylinder 16. If so, the ring 20 is received into a concave part 23 of the bracket 22, a switch 27 operates, a coupling pin 24 is inserted into a through hole 25 of the ring 20 and the bracket 22, the rod 19 and the bracket 22 are automatically coupled together, and the cabin 4 is tilted forward as centering on a fulcrum 10.