The present invention enables a member to be accurately fixed to a floor. With tapped holes 5 in a member mounting section 2 accurately aligned with marks formed in a grating 20 so as to correspond to through-holes 9, a bolt 14 is screwed in an internal thread cylinder 23 (fixed in a vent hole 21 in the grating 20) through a through-hole 13 in a presser plate 12 that can have its position changed relative to the member mounting plate 2, and the presser plate 12 is used to fix the member mounting plate 2 to the grating 20.