Abstract: A tube 12 made of stainless steel is arranged in a thermal bath 13 and an AC current is supplied to the tube to apply an AC heat directly to the tube and a liquid sample contained therein. An AC temperature of the tube 12 is detected by a thermocouple 19. An amplitude of the AC heat, and a phase difference between the AC heat and the AC temperature are detected. The above measurement is performed for the vacant tube, the standard liquid sample containing tube and the liquid sample containing tube to derive amplitudes .DELTA.T.sub.c, .DELTA.T.sub.r and .DELTA.T.sub.s and phase differences .phi..sub.c, .phi..sub.r and .phi..sub.s. Then, a heat capacity .rho..sub.s .multidot.C.sub.s per a unit volume of the liquid sample is calculated from a following equation.rho..sub.s .multidot.C.sub.s =[{sin (.phi..sub.s)/.DELTA.T.sub.s -sin (.phi..sub.c)/.DELTA.T.sub.c }/{sin (.phi..sub.r)/.DELTA.T.sub.r -sin (.phi..sub.c)/.DELTA.T.sub.c }].rho..sub.rwherein C.sub.r and .rho..sub.