Provided are a portable input device for inputting coordinates, a method of calibrating the device, and a computer readable recording medium storing a computer program for making a computer perform the method. The portable input device includes two digital cameras, a calibration tool, a storage section, and a controller for calculating coordinates of an object on an input surface based on images taken by the two digital cameras based on images taken by the two digital cameras so as to include the calibration tool. The controller also calibrates positions and widths of a detection band which corresponds to a detection zone defined in a vicinity of the input surface. The positions and the widths of the detection band are stored in the storage section in relationship to positions on the input surface.