Experimental and analytical discussions were performed concerning the transient characteristics of evacuated glass tube collectors exposed to the periodic variation of insolation. The basic equations derived from the collector model were transformed into finite difference equations. The numerical results by the FDM agreed quite well with the experimental results, and the adequacy of the physical model was confirmed. Then, to discuss the thermal characteristics of the evacuated glass tube collectors more generally, the effects of eleven nondimensional parameters, which constituted the basic equations, and the effects of principal physical quantities on the collector efficiency and on the amplitude of the outlet water temperature variation were clarified.