A marker according to the present invention is formed of a translucent material, and comprises at least: a plurality of protruding surfaces arranged in a first direction; and a plurality of portions to be detected which are arranged at positions on the reverse side to the plurality of protruding surfaces and which are projected, as optically detectable images, onto the plurality of protruding surfaces. Each of the cross-sectional shapes of the plurality of protruding surfaces in a cross section in the height direction of the marker along the first direction is a curved line having a curvature radius which increases with increase in a distance from the vertex of the curved line.