To reliably detect that a server can not receive an image when transmitting the image to the server from a diagnostic device, thus eliminating a user's unnecessary waiting time, in a medical image network system conforming to the DICOM (Digital Imaging and Communication in Medicine) standards and the like.

The diagnostic device periodically transmits a C-ECHO request command to the server 11 for inquiring the possibility of image reception, recognizes that image transmission is possible if there is a response from the server 11, and displays an error if not. When an image transmission instruction is input and only when the diagnostic device recognizes that the image transmission is possible, the image is transmitted to the server 11.