To prevent an errneous of a preceding document by not performing jam detection until the rear end of the preceding document passes a read position in case the preceding document is passing the read position at the time of detecting that the tip of a succeeding document is in a specified position.

In case a document is being read, it is so judged that the document is passing slit glass, and whether a register sensor (tip detecting means) is off is discriminated (S4). In case the register sensor being off, whether the rear end of the document has passed a read position is discriminted on the basis of the pulse count value of a driving motor counted from the position of the register sensor (S7). In case of having passed, whether the register sensor is turned on again is discriminated (S8). In case of the register sensor being on, it is so judged that a succeeding document is conveyed in a somewhat jointly fed state, and the conveyance of the preceding document is continued without performing jam detection to make the document pass through the read position.