To provide an entrance execution method for a bathroom unit capable of connecting the drain hole of a door lower frame and a drain pipeline even when the underfloor gap is small.

A drain pipeline is installed under a washing place floor or the floor of an adjacent room in advance so that its drain inlet faces the door installation section of a bathroom provided between the washing place floor of the bathroom and the floor of the adjacent room of the bathroom from below. A trough-like drain reception section receiving the threshold section of the door from below and receiving the hot water or water flowing into the threshold section side from the bathroom is received by the drain inlet and/or the peripheral edge of the drain inlet so that the drain hole provided on the drain reception section faces the drain inlet. A process for connecting the drain hole and the drain inlet in a watertight state can be conducted by only the work on the floor.