Abstract: Video data signals which are generated from a portable image scanner and temporarily stored in a shift register in an interface circuit are transferred to an external image processing device such as a word processor through a switching circuit which turns on upon reception of a transfer permission signal from a latching circuit for validating scanning condition. Since the transferring of the video data signals to the image processing device are effected without being controlled by the image processing device, it can be performed at high speed without causing a scanning error even if the sub-scanning speed is rather increased.