In connection with an error event detected in an image forming apparatus, a fault diagnosis service server diagnoses the error event and obtains a diagnosis result for handling to be performed on the error event detected in the image forming apparatus. In a case where the diagnosis result indicates a plurality of candidates for handling to be performed on the error event, the fault diagnosis service server compares the plurality of candidates for handling to a result estimated by a diagnosis model with respect to the error event. In a case where the plurality of candidates for handling is different from the result estimated by the diagnosis model, the fault diagnosis service obtains partial operation information from a history of the image forming apparatus and executes machine relearning based on the obtained partial operation information with respect to a layer in a latter stage of a plurality of layers included in the diagnosis model, each layer performing a different estimation.