PURPOSE: To take a thermal insulation test of a film used for a greenhouse, etc. in indoor with good reproducibility, by measuring the heat transmission coefficient.

CONSTITUTION: A hot air blower 15 provided in a heat generation chamber 12 performs heat generation of QHkcal/h and hot air is circulated to hold the temperature in the chamber constant at Tin. Then, radiative conduction of Q1kcal/h to a black board 14 cooled to specific temperature is carried out through the film to be tested, and convection heat conduction of Q2kcal/h (at temperature Tout) by dry air flowing in an air channel chamber 13 is attained. Further, heat conduction of QWkcal/h is performed through a heat insulating material 16. The sum of the Q1, Q2 and Q3 is equal to the QH. Then, the coefficient kcal/m2. h.°C of overall heat transmission of the film is shown by an equation in a figure, where A is the area of the tested film 10. In this case, the QH is obtained through an integrating meter, the QW is calculated, and the Tin and Tout are obtained through thermometers, so the calculation of said equation is analyzed by a data analyzer.