PURPOSE: To provide a built-in storage device which may be handled by aged persons and which may contribute for reduction of the cost of a threshold by setting the heights of the upper surface of the threshold or the upper surface of a base plate from the bottom surface of the built-in storage device at heights lower than a predetermined height.

CONSTITUTION: A threshold 3 is laid at the entrance of a built-in storage device such as a closet A2 or the like adjacent to a Japanese style room, and a base plate 51 is laid on the bottom thereof, the heights of the upper surface of the threshold 3 and the upper surface of the base plate 51 being set so as to be lower than 30mm from the bottom surface. In this case, tatami mats having a height lower than 30mm can be laid in the Japanese style room adjacent to the storage device, and accordingly, a height difference between the Japanese style room and an European style room may be eliminated so as to give a structure which can be easily handled by aged persons. Further, a spacer 6 is laid in the lower part of the threshold 3 so as to set the heights of the upper surface of the threshold 3 and the upper surface of the base plate 51 at 50 to 70mm from the bottom of a closet A3. In this case, a threshold 3 having a height lower than 30mm may be used as a normal threshold. That is, the mass-production can be made so as to contribute the cost of the threshold.