The present climate of Mars is extremely cold and dry, and is characterized by a very thin CO2 atmosphere. On the other hand, geological evidence suggests that the Martian climate in the past might have been warm and wet, suggesting that the atmospheric CO2 pressure would have been several bars higher. However, the fate of the abundant CO2 is still unclear. Here we propose a possible scenario for the evolution of CO2 on Mars. Numerical results suggest that CO2 in the early atmosphere would have reduced by a runaway condensation to form large CO2 ice caps. Then, the large CO2 ice caps should have shrunk by basal melting and most of CO2 has percolated into subsurface of the ice caps. The CO2 would have formed clathrate hydrate and carbonate minerals, and may still reside in the subsurface of Mars. This could explain the apparent shortage of CO2 on the present Martian surface.