An input apparatus, comprising: a display element having a display screen of a predetermined size; a first sensor configured to have a detection area that is smaller than said display screen, and to detect coordinates of a pointing position pointed to in the detection area by a pointing body, wherein said first sensor is coupled with said display screen such that said detection area, in which a pointing position pointed to by said pointing body is detected, maps to a predetermined display area within said display screen; a second sensor arranged on a front surface side of said display element and configured to detect a pointing position pointed to by the pointing body, wherein the second sensor has a detection area corresponding to the entire area of the display screen, wherein said first sensor includes a circuit being configured to attach identification information for identifying the first sensor to pointing input detection information supplied from the first sensor, wherein identification information for identifying the second sensor is added to pointing input detection information supplied from the second sensor, wherein said first sensor is transparent or translucent, wherein said first sensor is detachable from the front surface of said display screen, wherein said input apparatus further includes a control block and said control block is configured to display positioning markers (601, 602) on said display screen for indicating a position at which the first sensor is to be attached, wherein said first sensor comprises positioning markers (801, 802) corresponding to said positioning markers (601, 602) of the display screen, wherein, after said first sensor is positioned to said positioning markers (601, 602) of said display screen and a user input pointing at said positioning markers (601, 602) is received, the control block is configured to determine whether the pointed position is correctly positioned or not by referencing the pointing input detection information supplied from the second sensor. a display element having a display screen of a predetermined size; a first sensor configured to have a detection area that is smaller than said display screen, and to detect coordinates of a pointing position pointed to in the detection area by a pointing body, wherein said first sensor is coupled with said display screen such that said detection area, in which a pointing position pointed to by said pointing body is detected, maps to a predetermined display area within said display screen; a second sensor arranged on a front surface side of said display element and configured to detect a pointing position pointed to by the pointing body, wherein the second sensor has a detection area corresponding to the entire area of the display screen, wherein said first sensor includes a circuit being configured to attach identification information for identifying the first sensor to pointing input detection information supplied from the first sensor, wherein identification information for identifying the second sensor is added to pointing input detection information supplied from the second sensor, wherein said first sensor is transparent or translucent, wherein said first sensor is detachable from the front surface of said display screen, wherein said input apparatus further includes a control block and said control block is configured to display positioning markers (601, 602) on said display screen for indicating a position at which the first sensor is to be attached, wherein said first sensor comprises positioning markers (801, 802) corresponding to said positioning markers (601, 602) of the display screen, wherein, after said first sensor is positioned to said positioning markers (601, 602) of said display screen and a user input pointing at said positioning markers (601, 602) is received, the control block is configured to determine whether the pointed position is correctly positioned or not by referencing the pointing input detection information supplied from the second sensor.