A thermal analyzer heats and cools a sample placed inside a furnace for measuring a thermal characteristic of the sample during heating and cooling. The thermal analyzer has a multilayer structure for covering the furnace and its surroundings so as to isolate the furnace and its surroundings from an external environment. The multilayer structure includes a multilayer wall with two layers formed of a material having high thermal conductivity and heat dissipation property. The two layers are spaced apart from one another to provide therebetween an interlayer that contains a substance having a heat capacity substantially equal to a gas contained in the furnace so that heat transfer between the two layers is minimized.