This research aims to abtain fundamental data with which to develop chemical heat-pump systems utilizing the decomposition and synthesis reaction of methyl formate. Chemical equilibrium analysis of the decomposition and synthesis reaction of methyl formate under vapor-liquid equilibrium was applied to the flow system experimental data. The chemical equilibrium of the decomposition reaction was measured between 0.6 MPa and 1.5 MPa for the temperature range between 283 K and 343 K. The chemical equilibrium of the synthesis reaction was measured between 3.0 MPa and 5.0 MPa for the temperature range between 333 K and 393 K. By comparing the experimental values with the calculated values of chemical equilibrium under vapor-liquid equilibrium, it was found that the decomposition reaction reached equilibrium at about 343 K and the synthesis reaction reached equilibrium at about 393 K.