To provide a sash glass screen misalignment prevention capable of simplifying the structure, being easily mounted even to the existing sash window frame and surely preventing the up-lift of the glass screen.

A hollow guide hole 15 forming a tapered surface 20 in the middle part of a square columnar block 14 is provided to form a holding block 11, the holding block 11 is inserted from an opening section 18 of a square cylindrical case 12 in an insertable manner, at the same time, a screw hole 19 passing through the bottom of the square cylindrical case 12 is formed therein, a screw 13 is mounted in the screw hole 19 to insert it into the hollow guide hole 15, and the front end of the screw 13 is brought into contact with the tapered surface 20 of the guide hole 15 to move the holding block 11 right and left.