To provide a retreating displacement suppressing mechanism capable of positively detaching a pedal bracket by operating a detaching mechanism even when a cowl top panel and dash panel retreat together.

In the retreating displacement suppressing mechanism for the operation pedal, a front end part 9a of the pedal bracket 9 swingably supporting the suspended operation pedal 11 is connected to a vehicle cabin side of the dash panel 5 partitioning an engine room 1 and a vehicle cabin 3, a rear end part 9b of the pedal bracket is attached to the cowl top panel 7 arranged above the dash panel via the detaching mechanism 13, and a regulating means 15 is provided in a vehicle cabin inner side facing the cowl top panel 7.