PURPOSE: To provide a lid with a heat sensitive indicator for a sample container which can be stored stably at normal temperatures, is set into a state to monitor temperatures in a simple mechanism and is highly accurate.

CONSTITUTION: A hollow in the lower part of a cylinder 4 is a lid to be fitted into a head part of a sample container 9. A colored substance 6 melted by heat is stored in a recessed part 3 of the cylinder 4 shut by a thin foil 7. A penetration layer 2 is arranged in touch with an outer surface of the thin foil 7 and a projection 1 to be connected to the sinkable head part extends to the vicinity of the thin foil 7 through a hole of the penetration layer 2. When the projection 1 is pressed to fit the hollow in the lower part of the cylinder 4 into the sample container 9 containing a dispensed sample or blood, a sharp edge of the projection 1 breaks the thin foil 7. As the temperatures rise, the solidified colored substance 6 is melted to penetrate to the penetration layer 2 via the projection 1.