The sealing characteristics between a turned surface of soft material such as copper and a smooth seal face of a rigid steel ball in static contact were investigated. This seal face received not only normal force but also tangential force. The following results were obtained from calculations by using a model that considered a surface roughness on a turned seal face as a wedge-like projection, and gas leak tests. (1) The compressive force for sealing, Pc/l, decreased with a decrease in the conical half angle, θ of seal face. In the case of a surface roughness of 8 μm, the value of Pc/l at θ=15° was about 0.4 times that at θ=60°. (2) The recommended values of θ were in the range from 5° to 35°, and the Pc/l values corresponding to the range were able to be forecast.