A detecting apparatus for determining whether liquid crystal glasses are displaced in a cartridge is disclosed. The detecting apparatus includes: a signal sensing device for sending sensing signals to an internal of the cartridge and for receiving the reflected signals from the internal of the cartridge; a reflector installed in the internal of the cartridge for receiving the sensing signals from the signal sensing device and for reflecting the sensing signals back to the signal sensing device; and wherein a determination of whether the liquid crystal glass is displaced in the cartridge is made by determining whether the reflected signals from the reflector are received after the sensing signals are sent. Upon determining whether liquid crystal glasses are displaced in the cartridge, impurities are prevented from getting into the cartridge and thus the cleanliness is enhanced and the labor power is reduced.