An image forming system, charaterized in that it includes: a user terminal having a first vibration-detection sensor and a first storage device; an image-forming apparatus having a second vibration-detection sensor and a second storage device; and a relay device having a third storage device, and that after job data that is stored in the first storage device and vibration-detection information of the first vibration-detection sensor that are received from the user terminal are registered in the third storage device, transmits the job data to the image-forming apparatus; wherein the image-forming apparatus is configured to: register the job data in the second storage device, and according to a request from the relay device, transmit the job data that is registered in the second storage device and vibration-detection information of the second vibration-detection sensor to the relay device; and the relay device is configured to: compare the amount of data of the job data that are received from the user terminal and registered in the third storage device with the amount of data of the job data received from the image-forming apparatus, and when there is difference between the compared data amounts, registers trouble information that indicates that there is the difference, related to the second storage device in the third storage device, wherein the relay device is further configured to: when the vibration-detection information of the first vibration-detection sensor that is stored in the third storage device and the vibration-detection information of the second vibration-detection sensor received from the image forming apparatus indicate that vibration is equal to or less than a threshold value, not compare the amount of data of job data received from the user terminal and stored in the third storage device with the amount of data of job data received from the image-forming apparatus. a user terminal having a first vibration-detection sensor and a first storage device; an image-forming apparatus having a second vibration-detection sensor and a second storage device; and a relay device having a third storage device, and that after job data that is stored in the first storage device and vibration-detection information of the first vibration-detection sensor that are received from the user terminal are registered in the third storage device, transmits the job data to the image-forming apparatus; wherein the image-forming apparatus is configured to: register the job data in the second storage device, and according to a request from the relay device, transmit the job data that is registered in the second storage device and vibration-detection information of the second vibration-detection sensor to the relay device; and the relay device is configured to: compare the amount of data of the job data that are received from the user terminal and registered in the third storage device with the amount of data of the job data received from the image-forming apparatus, and when there is difference between the compared data amounts, registers trouble information that indicates that there is the difference, related to the second storage device in the third storage device, wherein the relay device is further configured to: when the vibration-detection information of the first vibration-detection sensor that is stored in the third storage device and the vibration-detection information of the second vibration-detection sensor received from the image forming apparatus indicate that vibration is equal to or less than a threshold value, not compare the amount of data of job data received from the user terminal and stored in the third storage device with the amount of data of job data received from the image-forming apparatus.