A pen input device sheet, which contacts a tip part of a core body of an electronic pen for a pen input device, includes a resin film layer. A diameter of the tip part is SR. An amount of sinking of the resin film layer is δ and a coefficient of kinetic friction between the resin film layer and the tip part is μ, which change according to a load when the tip part is in contact with the pen input device sheet. When the load applied to the tip part of the core body is changed and corresponding measurements are taken, and the measurements plotted with μ allocated to an ordinate axis and a ratio of δ/SR is allocated to an abscissa axis, a fitted straight line plotted based on the measurements has a proportional relation corresponding to a proportional relation between μ and the ratio of δ/SR.