PURPOSE: To reduce the heat quantity transmitted from the heat of outside air to a transparent member of an observation window with convection by attaching a heat transmission inhibiting plate of a specific structure to the surface of the observation window in a box for regulating temperature having the observation window partitioned with the transparent member on one surface and parts other than the window and the other surfaces covered with a heat insulating material.

CONSTITUTION: In a box for regulating temperature having an observation window 1 partitioned with a transparent plastic member 16 so as to enable observation of the interior on one surface and parts other than the observation window 1 on the one surface and other surfaces covered with a heat insulating material 12, the surface of the observation window 1 is provided with a heat transmission inhibiting plate 2, composed of a heat insulating material 19 and having plural holes 18 of a size without interrupting observation of the interior at a depth providing loose bonds of a gas between the respective holes 18.