To provide a thermostatic box wherein the interior can be kept at a temperature suitable for storage at a normal temperature and the structure is simple and inexpensive, and to provide a method for preserving an article using the box.

As a heat accumulating agent 3b, a substance with a melting point of 17.4°C is used, and each regenerator 3 with the agent 3b frozen or thawed is received together with an arbitrary article A in a box 1. Thus the interior of the box 1 is kept at a temperature close to the melting point of the agent (approximately normal temperature) by the heat accumulating agent 3b. This is advantageous for transporting an article which must be preserved at the approximately normal temperature instead of a low or high temperature, such as some kinds of medicine and organism parts. In addition, since the interior of the box 1 can be kept at an aimed temperature by the agent 3b comprising a single substance, the structure is simple and inexpensive to construct.