PROBLEM TO BE SOLVED: To detect the presence of snow cover inexpensively, accurately, and extensively so as to make it possible to prevent collapse or the like of a greenhouse by snow cover.SOLUTION: In detecting snow cover of a greenhouse roof 14 in which temperature is managed by a heating device, the inner surface temperature (the surface temperature of a greenhouse side) of the greenhouse roof is measured by a temperature sensor 40, and when the fluctuation in the inner surface temperature of the greenhouse roof which is measured by the temperature sensor is within a given range, it is detected that there is snow cover on the greenhouse roof. When the temperature sensor is disposed at a plurality of positions and the number of the temperature sensors indicating a value within a given threshold range is not less than a given number, it can be detected that there is snow cover.SELECTED DRAWING: Figure 4
