PURPOSE: To realize resistance against repetitive sterilizations with heat, chemicals or the like and to enable minimization of thickness by forming in a structure in which a window glass is sandwiched between welded metal plates.

CONSTITUTION: The sheath for hard endoscope is provided with windows 51W to 53W each having a structure in which window glasses 51 to 53 are sandwiched between at least two layers of welded metal plates 50 and 54, in other words, the window glasses 51 to 53 are mounted by a mechanical means. These window glasses 51 to 53 are completely free from peeling off, degradation or the like because of repetitive sterilizations with heat, chemicals or the like. In this structure, as the sheath is in such a relatively simple structure that the metal plates 50 and 54 are welded at least in two layers and the window glasses 51 to 53 are sandwiched by the metal plates 50 and 53, it is easy to reduce the thickness and size of the sheath.