PURPOSE: To certainly discriminate the outer diameter sizes or surface states of bottles at the predetermined height thereof.

CONSTITUTION: When bottles B1, B2 traverse a discrimination area formed by light projectors 11, 12 and photodetectors 21, 22, the quantities of lights detected without being blocked by the bottles B1, B2 are measured and the min. values thereof are compared to discriminate the outer diameter sizes of the bottles B1, B2 and the change degrees of the quantities of lights received after transmitted through or reflected from the bottles B1, B2 are compared to discriminate the surface states of the bottles B1, B2. Since the incident positions of light to the photodetectors 11, 12 are not related at all, even if the bottles B1, B2 are shaken during transfer, the outer diameter sizes or surface states of the bottles B1, B2 can be certainly discriminated and, since it is unnecessary to discriminate the bottles as a whole, the light projectors and the photodetectors can be miniaturized and can be produced at low coast.