An auto calibration method of an infrared sensor module (21A, 21B, 21C) for correctly sensing touch in case a deviation of the infrared sensor module (21A, 21B, 21C) occurs with respect to an optical signal region which actually receives optical signals arising from light emitted from an infrared light emitting portion and reflected by retro-reflection plates in an optical sensing frame, wherein the infrared sensor module (21A, 21B, 21C) includes a sensor block with a light receiving region and is perpendicular to a touch surface of a display panel, wherein the light receiving region is divided into m x n blocks, wherein m and n are natural numbers greater or equal to two, wherein the blocks are arranged in m rows and n columns, wherein each of the blocks has a plurality of light receiving pixels arranged in one and the same row; the method comprising: Turning on the infrared sensor module (21A, 21B, 21C); Scanning the optical signals of each block per each of the m rows; Comparing with each other the optical signals of the blocks in each of the n columns; Selecting for each of the n columns, the one or more blocks having maximum output optical signals compared to the other blocks in the same nth column, wherein when plural blocks are selected from each of the n columns, adjacent blocks in different rows are selected; Activating the blocks which are selected and deactivating the blocks which are not selected so as to assort the blocks, Setting the activated blocks as a Region of Interest and Ending the auto calibration; wherein the summed output of the optical signals of the light receiving pixels on a per column basis of the one or more selected blocks is used to measure the optical signals for sensing a touch position at the touch surface of the display panel after the auto calibration. wherein m and n are natural numbers greater or equal to two, wherein the blocks are arranged in m rows and n columns, wherein each of the blocks has a plurality of light receiving pixels arranged in one and the same row; the method comprising: Turning on the infrared sensor module (21A, 21B, 21C); Scanning the optical signals of each block per each of the m rows; Comparing with each other the optical signals of the blocks in each of the n columns; Selecting for each of the n columns, the one or more blocks having maximum output optical signals compared to the other blocks in the same nth column, wherein when plural blocks are selected from each of the n columns, adjacent blocks in different rows are selected; Activating the blocks which are selected and deactivating the blocks which are not selected so as to assort the blocks, Setting the activated blocks as a Region of Interest and Ending the auto calibration; wherein the summed output of the optical signals of the light receiving pixels on a per column basis of the one or more selected blocks is used to measure the optical signals for sensing a touch position at the touch surface of the display panel after the auto calibration. Turning on the infrared sensor module (21A, 21B, 21C); Scanning the optical signals of each block per each of the m rows; Comparing with each other the optical signals of the blocks in each of the n columns; Selecting for each of the n columns, the one or more blocks having maximum output optical signals compared to the other blocks in the same nth column, wherein when plural blocks are selected from each of the n columns, adjacent blocks in different rows are selected; Activating the blocks which are selected and deactivating the blocks which are not selected so as to assort the blocks, Setting the activated blocks as a Region of Interest and Ending the auto calibration; wherein the summed output of the optical signals of the light receiving pixels on a per column basis of the one or more selected blocks is used to measure the optical signals for sensing a touch position at the touch surface of the display panel after the auto calibration.