In order to provide a means to uniquely estimate the attitude in a wider range of angles to thereby realize a more accurate attitude estimate, a planar marker is provided. The planar marker includes a planar visual marker having a two-dimensional pattern code and at least two attitude inversion detection patterns Fx and Fy each consisting of a transparent cylindrical body having a pattern on the side face within the range of 180 degrees around the central axis ra and being provided so as to be orthogonal to each other on the same plane as that of planar visual marker. A marker is provided that includes at least one attitude inversion detection pattern. The attitude inversion detection pattern consists of the planar visual marker and a transparent spherical body having a pattern on a hemispherical surface and is provided on the same plane as that of the planar visual marker.