To provide a method of measuring a solution temperature heated by microwaves, a method of measuring/controlling the temperature of a reaction liquid in a reaction apparatus using microwave, a reaction apparatus using microwaves having the method of measuring/controlling, and a method of manufacturing copper phthalocyanine using the method of measuring/controlling and the reaction apparatus, without using expensive temperature measuring devices, at a low price, and with substantially necessary and sufficient precision.

The method of measuring/controlling a solution temperature heated by microwaves is characterized in that it uses a liquid expansion type thermometer enclosing a liquid having a loss coefficient (×tanδ), which is the product of the dielectric constant () and the dielectric loss angle (tanδ), of not larger than 3. The reaction apparatus using microwaves has, within the apparatus provided with a heating device by microwaves, a vessel containing a chemical reaction liquid and the liquid expansion type thermometer enclosing a liquid having a loss coefficient (×tanδ), which is the product of the dielectric constant () and the dielectric loss angle (tanδ), of not larger than 3. The method of manufacturing copper phthalocyanine uses the reaction apparatus.