1. A method for detecting a two-dimensional code of three position detection patterns provided in positions corresponding to respective apices of a right angled isosceles triangle, and a data region is provided in a region defined by the position detection patterns, the method comprising: detecting a plurality of position detection patterns included in an image; identifying positions of the center points of the detected position detection patterns; selecting three center points that constitute apices of a right angled isosceles triangle from among the identified center point positions; extracting for a feature of a two-dimensional code from a two-dimensional code region defined by the position detection patterns corresponding to the selected center points, or a peripheral region thereof, and determining whether a two-dimensional code exists in the two-dimensional code region when the feature of a two-dimensional code is extracted.