To facilitate manufacturing of a structure in which a drain pipe is connected to a drain main body part such as a drain pan, enable a manufacturing cost thereof to be reduced, also prevent residual water that cannot be drained from being generated and prevent mold and rust or the like from being generated and at the same time to enable all various problems concerning freezing of residual water to be eliminated.

The drain pipe connection structure has a drain main body part 1 with a pan part 5 and a back-board wall 6 and provided with a drain hole 8 near a root part of the back-board wall 6, and a drain pipe 2 connected in consistent with the drain hole 8 of the drain main body part 1. The back-board wall 6 is provided with an arcuate flange 15 made under a burring work at the periphery of an opening of the drain hole 8, and the drain pipe 2 is outwardly fitted to the outer peripheral surface of the arcuate flange 15 and connected to the drain main body part 1.