ken on the lines 17A--17A and17B--17B in FIGS. 16A and 16B, respectively; FIG. 18 is a sectional view taken on the line 17B--17B in FIG. 16B for explaining how to fixedly hold the PC board by suction.In this embodiment the parts corresponding to those in Embodiment 1 are identified by the same reference numerals and no description will be repeated thereof.In FIGS. 16A through 18, reference numeral