The present invention implements efficient transmission of captured images while also maintaining high-resolution image quality. The present invention is an image processing method for an X-ray image diagnosis apparatus, the method including the steps of: obtaining the effective bandwidth for transmitting captured images; obtaining imaging conditions; calculating the respective resulting data amounts when a captured image captured under the conditions is compressed using lossless and lossy compression, mixing the captured images compressed losslessly and lossily, and determining the mix ratio so that the transmission amount per unit of time when multiple captured images are transmitted is less than the effective bandwidth; and transmitting the multiple captured images compressed losslessly and lossily at the determined ratio.