The confocal three-dimensional measurement is a method in which only the intensity values of the relative light at each measurement position are compared with each other and a point where the light intensity is highest is found to convert a three-dimensional height value, and thus, if a point where the intensity of light is greatest is accurately found by measuring the intensity of light more frequently only near a focal distance where the actual light intensity is greatest without continuously measuring the intensity of light at regular intervals during a measurement period, the amount of data from an image sensor to be processed can be reduced while maintaining precision or resolution of the three-dimensional measurement. That is, the image sensor measures the intensity of light at a low-rate frame level of several tens to several hundreds of frames without the need to continuously transmit image data measuring the intensity of light at several thousands of frames per second, and measures the intensity of light at a high rate of several thousands of frames per second from the time of entry into the measurement period determined as a maximum point of the intensity of light and stores the intensity of light in a DRAM memory buffer in the image sensor. Moreover, the image sensor operates again in a low-rate frame mode if determined to be out of the maximum point of the intensity of light and separately transmits low-rate frame data and data which has been stored in the DRAM memory buffer in the image sensor during low-rate frame time, to allow a control operation unit performing confocal three-dimensional measurement to find a point with the maximum intensity of light, such that the amount of image data transmitted from the image sensor during search time in the measurement period for the confocal three-dimensional measurement is reduced, thereby reducing the cost of the image sensor and the manufacturing cost of a confocal three-dimensional oral scanner using the im
