An image capturing system includes a cassette having a radiation detector, an image memory, and a cassette controller, an image capturing apparatus, a display device, and a host computer. The cassette controller comprises a capacity value transmitter for transmitting a capacity value of the radiation image information to the host computer before transmission process, and an image transmitter for transmitting the radiation image information. The host computer comprises an indicator controller for controlling the display device to display an indicator representing the capacity value received from the cassette as the upper limit, and a bar controller for controlling the display device to display a bar moving toward the indicator and having a length corresponding to the received capacity value of the radiation image information while the radiation image information is being received.