Disclosed are an intra-oral sensor, a cradle, and an intra-oral sensing system. More particularly, the present invention relates to an intra-oral sensor, a cradle, and an intra-oral sensing system, in which the intra-oral sensor can transmit projection data, can be charged with driving power, and can be sterilized at the same time when mounting the intra-oral sensor in the cradle, and can output the projection data including an identifier therein, thereby enabling an operator to easily recognize which part in a set of teeth is represented by image data corresponding to the projection data.