Thermal indicator

A heat sensitive indicator comprising:

• an elongated ampule bottle enclosing a colored heat-sensitive material that melts into a colored melt at a predetermined temperature,
• a rolled cylindraceous body of a composite membrane joining an absorbable membrane that absorbs the colored melt of the colored heat-sensitive material, onto one surface side of an impermeable membrane that is impermeable to the colored melt, so that the impermeable membrane is located inside the rolled cylindraceous body, and
• a tube inserting and sealing the ampule bottle into a space surrounded by the impermeable membrane of the cylindraceous body, through which a color of the absorbable membrane can be visibly recognized from the outside of the tube;
• wherein, after at least a part of the ampule bottle is broken below melting point of the colored heat-sensitive material to discharge or to make it possible to discharge at least a portion of the solid-state colored heat-sensitive material into the space surrounded by the impermeable membrane, the colored melt is absorbed through an edge portion of the absorbable membrane which is positioned at an edge surface of the cylindraceous body and then the solid-state colored heat-sensitive material is melted, a formed colored portion of the absorbable membrane can be visibly recognized from the outside of the tube.