Characteristic analysis was conducted for a LiBr-H2O vertical liquid film absorber installed with bare tubes, corrugated tubes or tubes with spirally wound fir-fins, the outer diameter of which is 12 mm. Calculation of local distributions of temperature and concentration of a falling LiBr aqueous solution and the absorption rate of water vapor into it showed that the fir-finned tube is superior to the other tubes. In addition, the effect of installation of multiple tubes was investigated under the condition of the total tube length of 4 m. The usage of one long tube without subdivision was found to give maximum values of heat generation and absorption rate of water vapor. Effects of vapor temperature and inlet temperature of cooling water circulating inside the tube were investigated for the tube with spiral fir-fins. Heat output, absorption rate of water vapor and heat output temperature increase linearly with an increase in the vapor temperature or a decrease in the temperature of circulating cooling water. The boost temperature as an increase of heat output temperature from the vapor temperature decreases with increasing the vapor temperature. It was confirmed that the LiBr-H2O heat transformer installed with fir-finned tubes will be able to generate heat output with boost temperature of 20-30 K when it is operated under the normal conditions of vapor temperature and/or inlet temperature of circulating cooling water.