To enable drain water to be positively discharged to an evaporating pan by a method wherein an extremity end of a drain pipe is provided with a hole which is smaller than a projection part of the drain pipe and larger than a concave part, a holding plate having a recess is inserted into the hole and drain water has flowed out of the drain pipe is passed to the holding plate through a drain guide.

An extremity end of a drain pipe 14a is provided with a hole 18 which is smaller than a projection 16 of a drain pipe 14a and larger than a concave part 17. A holding plate 15 having a recess 19 is inserted into the hole 18. Drain water has flowed out of the drain pipe 14a is passed to the holding plate 15 through a drain guide 20. With such an arrangement as above, assembling operation can be carried out only by inserting the drain pipe 14a into the holding plate 15 and the extremity end of the drain pipe 14a is freely rotated, so that it is possible to prevent twisting and deformation of the drain pipe 14a and the holding plate 15 when these members are fixed and further drain water can be positively discharged to an evaporating pan 10.