The present invention provides a marker that can uniquely estimate the posture within wide-angle range while maintaining the flatness, and a posture estimating method. The marker includes a two-dimensional pattern code and a posture detection pattern emitting different light depending on an observation direction of the pattern code at around the first axis on a two-dimensional plane formed by the pattern code. The method using the marker has a Step-1 of using a captured image of the marker to identify a color of the light or a pattern drawn by the light, Step-2 of determining, depending on the color or the pattern identified in Step-1, a posture of the marker at around the first axis, and a Step-3 of determining a posture of the marker depending on a positional relation between the posture at around the first axis determined in Step-2 and the elements constituting the captured image.