A check detector for the neck and finish portion of glass bottles is disclosed. The check detectors comprises means for rotating glass bottles successively conveyed to a fixed position and a slide block which can change position freely in the width direction and vertical direction of the bottle. A plurality of light emitters for illuminating the neck and finish potion of the glass bottle are mounted to the slide block. The light by from the plurality of the light emitters is converged to the illuminated region from difference directions, and there are a plurality of light receivers equipped with light sensors for detecting the light reflected by checks in the neck and finish portion of the bottle, the light reflected by the mold seam formed at the neck and finish portions, and the directly transmitted light passing through the neck and finish portion, via lenses mounted to the slide block. There is a light emitter control section for constantly operating a plurality of light receivers in the light emitting condition so that the reflected and direct light are input as data, wherein each of the light receiving elements are divided so as to correspond to the vertical position of the neck and finish portion. The data inputted as light reflected at the seam and the data inputted as the direct light transmitted through the neck and finish portions are deleted.