PROBLEM TO BE SOLVED: To address such problems that a conventional drain trap in a dental examination device is formed by screwing a water accumulation cup into a drain trap body, thereby requiring time and labor for attachment/detachment and that, when a filter is put therein, with it turned upside down, a screw is not fully fastened when attaching the water accumulation cup, thereby causing insufficient sealing.SOLUTION: The attachment/detachment of a water accumulation cup is facilitated by attaching the water accumulation cup to a drain trap body by an engagement part provided at an outer periphery lower part of the drain trap body and an engagement protrusion protruding to an inner wall of the water accumulation cup. A bayonet-type detachable part is provided at the lower end of a filter. The shapes of the upper and lower parts of the filter are differentiated so as to prevent erroneous attachment of the filter to the water accumulation cup.
