An image transmission apparatus transfers to an external apparatus data amount information indicating an amount of target image data and information of a priority order of the target image data. The apparatus also receives from the external apparatus a response signal indicating whether the external apparatus will accept transmission of the target image data in accordance with the data amount information, the information of priority order, and a free storage capacity to store the target image data in the external apparatus. Transmission of the target image data is controlled in accordance with the response signal.