PURPOSE: To see the locus of a hitted golf ball on a projection screen by constituting the projection screen, to which an image or the like is projected, of fine magnetic powdery materials and a DC magnetic field generating means which binds them into a plane shape.

CONSTITUTION: When a voltage and a current are supplied from a DC power source 8c to a winding 8b wound around an iron core 8a, the iron core 8a is excited in DC, and its magnetic poles 8a1 and 8a2 are magnetized to N and S to generate a magnetic flux from the N pole to the S pole. The distribution of this magnetic flux between N and S poles is determined by a magnetic circuit resistance; and when fine magnetic powdery materials 8d are scattered infinitely between these N and S poles from a supply device 8e, fine magnetic powdery materials are stuck to one another between N and S poles by the magnetic force to form rows of fine magnetic powdery materials 8d, and then, most of the magnetic flux passes in rows 8d1 of fine magnetic powdery materials, and as a result, fine magnetic powdery materials 8d are stuck to one another more strongly, and many rows 8d1 are formed into a plane shape.