When a transmission of image data to a destination has not been completed, retransmission processing in which the image data is repeatedly transmitted to the destination is performed and the number of times the transmission has been performed is counted. When the number is higher than a predetermined value, the sender is informed about the occurrence of transmission error and whether the modification of destination information has been requested is determined. When the modification has been requested, the destination information is modified; when the modification has not been requested, the destination information is deleted and then the deletion of the destination information is informed. When stored destination information including destinations of data is wrong, the use of the destination information is inhibited, which prevents users as recipients from feeling displeasure.