A film of a pen input device is provided, and a point determined by a combination of a static friction coefficient value x and a kinetic friction coefficient value y falls within a region including a line segment and the neighborhood of the line segment in a coordinate system showing the static friction coefficient on the X-axis and the kinetic friction coefficient on the Y-axis, the line segment being expressed as y=0.3071x+0.0496 0.26≧x≧0.13, the following conditions being satisfied: 0.16≧the static friction coefficient value x≧0.10 0.100≧the kinetic friction coefficient value y≧0.080, the size a, the height b, and the pitch c of concavities and convexities in the surface satisfying the following conditions: 20 μm≧a≧16 μm 0.9 μm≧b≧0.4 μm 30 μm≧c≧26 μm.