A high precision, rapidly operable optical parallelism measurement device includes a light source module, a light beam splitting module and at least two photoelectric detectors. The light source module has a light source and a light beam splitting element such that the light source module is able to produce two light beams perpendicular to each other. One of them is parallel to the moving direction, and is received by one of the detectors, while the other beam is split into two beams perpendicular to each other by the light beam splitting module. One beam is parallel to the former parallel by moving beam and is received by the other detector. With this scheme, the measurement can be performed by means of those perpendicular and parallel light beams without being affected by the structure of the machine platen to cause errors. The device can be manufactured with low cost and high precision. It is very compact in size and easy to carry and build up for rapid measurement.