PURPOSE: To make it possible to discriminate containers by forming the bottom of a container with concentric portions to be detected and by detecting the position and the number of the concentric portions.

CONSTITUTION: Concentric portions 2aW2d to be detected are formed in the bottom of a container. These grooves have different positions and numbers for the respective containers. On the other hand, a container discriminator 3, in which a container is placed, is equipped with detectors 4aW4d at a preset spacing toward the outside. Now, if the container 1 is placed in the discriminator 3, the impedance of the detecting coil is changed, and the resonant frequency of a resonant circuit is changed to increase the resonant current so that an output is generated at a voltage comparator 9. At this time, if there is no groove in the detected portion facing the detector 4b, the output of the comparator 9 is low. Thus, the output of the comparator 9 is changed in accordance with the existence of the grooves 2a and so on. As a result, the position and number of the grooves of the container can be detected so that the container can be discriminated.