31 generates 34 h 34 high level for v0 gt v1 and generates 34 l 34 low level for v0 lt v1 the ic32 is used for locking the output of the ic 31 since the signal s1 is input to the input terminal of the ic 32 at the start point of the automatic exposure control operation ae operation by the application of the signal s1 in other word when the output of the ic 31 is 34 h 34 at the period when the illuminating point of the fluorescent lamp 1 reaches just before the leading end of the original document the output of the ic 32 becomes 34 l 34 whereby 34 h 34 output of the ic 31 is maintained if the output of the ic 31 is 34 l 34 at the time of application of the signal s1 since the input terminal of the ic 32 becomes 34 l 34 and the output of the ic 32 becomes 34 h 34 whereby the output 34 l 34 of the ic 31 is maintained in the latter case when the signal s1 rises the voltage v0 corresponding to the light reflected from the white reflection region p disposed just before the leading end of the original document is lower than the standard voltage v1 the light amount reflected from.