1. A stereoscopic image display system comprising: an image display unit that displays a parallax image composed of a right eye image and a left eye image; a transmission portion for a right eye transmitting only the right eye image of the parallax image and a transmission portion for a left eye transmitting only the left eye image of the parallax image; a put-on/taken-off determination unit that determines whether glasses are put on or taken off; and an image generation unit that generates the parallax image when it is determined that the glasses are in a put-on condition by the put-on/taken-off determination unit, and generates only either of the right eye image and the left eye image of the parallax image when it is determined that the glasses are in a taken-off condition by the put-on/taken-off determination unit, wherein the put-on/taken-off determination unit comprises: an invisible light emission unit that emits light outside the visible region and a light reception unit for receiving the light, the invisible light emission unit and the light reception unit being disposed on the image display unit; at least three retroreflectors disposed on the glasses, at least one of which is disposed off a straight line; and a determination unit that calculates an inclination of the glasses, wherein the determination unit includes a pre-stored relative positional relationship of the at least three retroreflectors; the light reception unit obtains a plurality of images visualizing light reflected by the at least three retroreflectors; the determination unit calculates a calculated relative positional relationship of the at least three retroreflectors from the plurality of images; the determination unit calculates an inclination of the glasses by comparing the calculated relative positional relationship of the at least three retroreflectors with the pre-stored relative positional relationship of the at least three retroreflectors; and the determination unit determines that the glasses are in the taken-off condition when the inclination of the glasses deviates from a predetermined range, and determines that the glasses are in the put-on condition when the inclination of the glasses is within the predetermined range.