PURPOSE: To make a transparent ice without protrusion over a whole upper tray by providing a water reservoir formed at an interval from the side face of the tray at the side face of the part of a lower tray, and a water reservoir cover extended from the flange of the upper tray for covering the top of the reservoir.

CONSTITUTION: The top of a water reservoir 6 provided on a lower tray 2 is covered with a water reservoir cover 1g extended from an upper tray 1. Water surface of the reservoir 6 is not brought into direct contact with chilled gas to be higher at its temperature than that of the water surface of the other tray 1, and growth of ice is mostly delayed. Accordingly, even when the water surface of the tray 1 is all frozen, the water surface of the reservoir is not yet frozen, or the thickness of the ice is thin. The water of volumetric expansion due to the growth of the ice from the water surface of the tray 1 cannot be escaped, but concentrated at the reservoir of unfreezing state to raise the water surface level at the part or to break the thin ice on the surface of the reservoir to gush out. Thus, this part is eventually raised to eliminate the protrusion of the ice on the surface of the upper tray. Thus, the ice in the tray 1 is not whitened, and whitened ice remains only in the whitened ice remainder 4 and the reservoir 6 of the tray 2 in which completion of ice making is delayed.