To effectively avoid the fouling of a process device and damage caused by collision with other object and effectively inhibit vaporization of a process solution, in a volume-reducing process vehicle capable of reducing the volume of resin foam through the dissolving of the resin foam into the process solution.

The volume-reducing process vehicle includes: a body B mounted on a vehicle body frame F and having a closed space therein; a rear door Gr capable of opening and closing a rear opening Br formed in the body B; a process tank V retaining the process solution L therein and having agitation means K2 for the process solution; a charging device C provided inside the body B and capable of charging the resin foam w into the process tank V, with its input part Ci facing the rear opening Br in the body B and its output part Co facing the inside of the process tank V; and cooling means R for cooling the process solution L in the process tank V to inhibit vaporization.