Abstract: A precision calorimeter which comprises a heater, an agitator and a detection bath which are disposed in a temperature controlled bath and in which gaps formed between them are filled with a liquid; and a detection unit placed in the detection bath, a gap formed therebetween being filled with a liquid; the detection unit being comprised of a detection element, a pipe for passing a sample therethrough provided with a mixer and a reference heater which are arranged between metallic pieces.