To improve quality of coating and to reduce time and labor required for cleaning work for a drying oven by removing dust accumulated in the oven.

A base 7 running on a conveyer rail 6 laid under the floor out of an oven and a trestle 4 on which a work W is placed are formed separately up and down through a support 8 with a required height and the support 8 is passed through a slit 9 formed in the floor wall 3F of the drying oven 1 into the oven to move the work W in the oven and to dry it. In addition, when the floor face 3f is cleaned and a cleaning liq. is let to flow on the floor face 3f, the cleaning liq. flows down on the floor face 3f formed on an inclined face toward the slit 9 and while it washes dust accumulated on the floor face 3f away, it flows into dust recovery channels 16 and then, it is drained outside. Therefore, before the dust made to fall on the floor face 3f grows to such a size that generates failure of coating, the dust can be simply removed only by letting the cleaning liq. flow and quality of the coating can be improved.