To provide a heat insulating sleeve capable of enhancing heat insulation of a metal to be worked, when the metal to be worked subjected to the induction heating to the semi-melting temperature is conveyed to the next process such as a forging apparatus.

The heat insulating sleeve 1 is used when conveying an aluminum billet in a heat-insulated state after the aluminum billet is subjected to the induction heating to the semi-melting temperature, and formed in a hollow cylindrical shape. The heat insulating sleeve mainly includes ceramics, and includes an inner cylinder 11 capable of accommodating the aluminum billet and an outer cylinder 12 mainly composed of Ti which covers the outer circumferential side of the inner cylinder 11.