PURPOSE: To adapt a hot plate to high purity microanalysis in heating evaporation treatment by constituting the hot plate by arranging a heating device in a box-shaped housing made of transparent quartz and arranging a temp. controller and a power supply device to the outside of the housing.

CONSTITUTION: A hot plate 1 is constituted of a box made of thin transparent quartz opened at one side part 2 thereof and formed into a housing 4 having four legs 3 of the same material quality formed to the outside lower part thereof. The height dimension of each of the legs 3 is set so as to be capable of arranging a quartz tray 5 receiving endothermic ultrapure water or an evaporation tray 6 for treating a sample under the hot plate 1. Further, a heating device having a required heating element incorporated therein is introduced into the hot plate 1 from the opened side part 2 to be arranged in the housing 4 and a lead wire 9 equipped with a connection part 8 is led out of the heating device through the side part 2 to be connected to a slidac 10 to be extended to a power supply device 19.