in an image measuring device that performs , on a work piece to be measured , low brightness continuous illumination and one of stroboscopic illumination and continuous illumination with high brightness , a common high - brightness led is used , and driving circuits are switched between pseudo - continuous illumination and one of stroboscopic illumination and continuous illumination . in the pseudo - continuous illumination , an average brightness is reduced by pulse lighting . in the stroboscopic illumination , high brightness light is emitted instantaneously . the switching between the pseudo - continuous illumination and one of the stroboscopic illumination and continuous illumination may be performed by changing a lighting cycle of the high - brightness led .