The present invention provides a detection device for a cassette comprising at least one supporting unit, each supporting unit comprising a plurality of supporting brackets which constitute a supporting plane, wherein the detection device comprises a sensing mechanism for detecting whether position of each of the supporting brackets in each supporting unit is within a predetermined range. In the present invention, through detecting positions of the supporting brackets in the cassette, and then judging whether the positions of the supporting brackets in each supporting unit are in a preset range, a supporting unit in which there is one or more bracket supporting brackets whose positions are not in the preset range can be maintained in time, and therefore, damage to the glass substrate due to large error in positions of the supporting brackets can be prevented.