PURPOSE: To achieve a highly accurate measurement by an indirect method of heating a sample through a bath liquid by making a temperature sensing section of a thermometer equal to a glass tublet containing the sample in the shape and the size.

CONSTITUTION: A glass tube 1 contains a sample 2 and a glass tublet 3 identical to the glass tublet 1 has a temperature measuring contact 4 of a thermocouple made of a fine strand.A heating bath liquid 5 is placed in a transparent vessel 6. The bath liquid 5 is heated with a burner 7 while both the tublets 1 and 3 are heated on the same condition. It is checked visually how the sample is melted and the temperature is measured with a thermometer 10 provided following the tublets. As the temperature sensing section of the thermometer and the sample are subject to the same condition, a highly accurate measurement of melting points can be done.