The invention provides an image transmission systemm, comprising: an image processing device having an image input portion, an image output portion, and a first wireless LAN communication portion; and a communicating device having an image transmission/reception portion and a second wireless LAN communication portion, wherein the image input through the image input portion is transmitted from thefirst wireless LAN communication portion of the image processing device to the communicating device and is then transmitted from the image transmission/reception portion to the external device, and wherein an image transmitted from the external device is received by the image transmission/reception portion of the communicating device, transmitted from the second wireless LAN communication portionto the image processing device, and output by the image output portion. Each of the image processing device and the communicating device includes: a first communication-setting-information memory portion; a second communication-setting-information memory portion; a first wireless connecting portion; a second wireless connecting portion; and a communication control portion.