To surely specify a reflecting face in the image information reader that conducts shading correction by using shading correction data in response to each reflecting face of a rotary polygon mirror.

A start signal detection circuit 21 detects a start point signal SOSL denoting a start point of main scanning of a light beam 34 to obtain a horizontal synchronizing signal HSYNCL and an index signal detection circuit 24 detects an index signal PINDEX denoting a reference reflection face of a rotary polygon mirror 36. A reset pulse CLRL is generated, which is at L in a leading of the index signal PINDEX and at H in a leading of the horizontal synchronizing signal HSYNCL and a pulse generating circuit 25 generates a mask signal MSKH that is contained in an active period L of the reset pulse CLRL. The mask signal is given to a clock input terminal 28a of a face management counter 28 to give the reset pulse CLRL to a reset terminal 28b.