jedec tray 93 containing the ic chip 31 is curved or if the package of the ic chip 31 is defective there may be the case of the change in the positional relation distance between the laser sensor 40 the laser light source 41 and the ccd sensor 42 and the z direction height direction of the ic chip 31 this may result in the fear that the apex position of the solder ball 33 or the substrate surface 31 a of the ic chip 31 is out of the partially scanned range w and the height of the solder ball 33 can not be measured the apparatus 10 employs the following counter plan in order to previously avoid the occurrence of the above mentioned problem that is easily susceptible to occur in the partially scanning method as shown in fig1 a to 11 c when the picture in the partially scanned range w is photographed the distribution in the height direction z direction of the dot number implying the detection of the value of one bit indicative of the light emission is detected is measured in each photograph picture for example the photograph picture the partially scanned range w.