To provide an intravital embedding instrument which reduces nonuniformity in a temperature distribution as much as possible, being generated on the outer surface of the instrument by heat generated in the instrument, uniforms the temperature distribution, and also reduces the maximum value in a temperature rise.

The instrument includes: a hollow case; and a storage body which is stored inside the case, and generates heat in an operation. The case is formed by a lamination material 20 comprising: an outer layer 21 formed of a highly biocompatible material to be brought into contact with a living body; an inner layer 23 formed of a material with good heat conductance; and an intermediate layer 22 between the outer and inner layers, formed of a high insulation material.