Abstract: The golf trainer apparatus includes a ball start portion which is on a ball launch site, a green mat, a main body having a ball entrance opening and exit opening, and an internal collection path of the ball injected into the ball entrance opening, an optical sensor for detecting the ball injected into and passing through the ball entrance opening, an algorithm processor for computing the speed of the ball detected by the optical sensor, and retrieving and outputting a predetermined putting distance on an actual green condition according to the computed ball speed, in which algorithm data with respect to ball putting distances obtained by applying a rolling resistance on the actual green for each ball speed is stored in a memory, and a digital distance indicator for indicating the data output from the algorithm processor in dimension of a distance unit.