We have developed downsizing a piston-cylinder clamp-cell to measure a specific heat under pressure using a commercial Differential Scanning Calorimeter (Shimadzu DSC-60 plus). The downsized cell with a diameter of 6.0 mm and a height of 5.0 mm has been achieved by a simplification of the cell design and using a high-yield-strength alloy of β-Titanium (KOBELCO, KS15-5-3). The cell allows us to achieve pressures of 0.7 GPa at room temperature as our designed value. As a demonstration of the cell, we have measured the specific heat anomaly due to the first-order transition at around 357 K in Ca2RuO4. The pressure variation of the transition temperature indicates that our cell allows us to achieve pressure of ∼0.3 GPa. Moreover, we have estimated that a heat capacity of ∼0.6 mJ/K is fully possible to measure within β-Titanium cell as absolute accuracy.