PURPOSE: To safely and surely block the tray groove of a partition wall to which the connection flange of a double tray is inserted.

CONSTITUTION: A guide rail 18 whose lower wall center is opened is provided solidly on the upper part of the tray groove 15 provided on the partition wall 6 which separates a heat insulating chamber 7 from a cold reserving chamber 8, and an elevation rail 19 made of heat resistance synthetic resin is arranged on the guide rail 18. A projected line 19b suspended to the tray groove 15 passing through the opening 18a of the guide rail 18 and a flexible fin 19c coming in contact elastically with the upper wall of the guide rail 18 and which presses the projected line 19b in the direction of the tray groove 15 are provided on the elevation rail 19.