The present invention relates to a golf training device capable of forming a two-dimensional, single planar and total symmetrical optical sensor net for detecting movement of a golf ball. The device comprises a square frame which has a signal producing means holding part on the first horizontal and the first vertical sides of the frame and a signal detecting means holding part on the second horizontal and the second vertical sides of the frame. On the signal producing means holding part, a light signal producing means including a light signal emitting means is installed to generate a two-dimensional, single planar optical path net. A light signal detecting means is spatially arranged in the opposite sides of the frame in accordance with the light emitting means to form a totally symmetrical optical sensor net for detecting the light signals from the light signal producing means. The present invention also includes a golf ball sensor means for detection of the golf ball movement at its initial impact and a data processing and display means which receives and processes output signals from the light signal detecting means for calculating the golf ball's take-off speed, the horizontal and vertical angles, and the trajectory distance. The square frame can be modified to an "U" or "II" shape to eliminate the upper frame of the sensor net and to reduce the dimensions of the training device.