PURPOSE: To make it possible to simultaneously and certainly clean both surfaces of an object to be washed, by forming the support jig of the object to be cleaned irradiated with ultraviolet rays from a material pervious to ultraviolet rays.

CONSTITUTION: An ultraviolet lamps 4 with mirrors 5 are provided to the upper and lower parts of the irradiation chamber 3 in the irradiation box 2 mounted in an apparatus case 1 to irradiate the center of the chamber 3 and the upper and under surfaces of the box 2 is cooled by fixed cooling water paths 6. A large number of objects to be cleaned, for example, a quartz vibrators 7 are arranged on a support jig 8 made of quartz and supported at the central part of the chamber 3. O2-containing gas is supplied to the chamber 3 through the sucking orifice 9 of the box 2 to exhaust internal gas from an exhaust orifice 10 along with a contaminant. When the lamps 4 are lighted, both upper and lower surfaces of the vibrators 7 are irradiated with ultraviolet rays and nascent oxygen is formed in the vicinity of said vibrators 7 to decompose a contaminant but, because the support jig 8 is pervious to ultraviolet rays, rays from the lamps 4 are not blocked by said support jig 8. Therefore, the surfaces of the vibrators 7 are uniformly irradiated to be uniformly cleaned.