A diagnosis device includes a first acquiring unit acquires, from a target device, context information corresponding to a current operation; a second acquiring unit acquires detection information output from a detecting unit that detects a physical quantity that changes according to operations performed by the target device; a first transmitting unit transmits the acquired context information to a learning device; a second transmitting unit transmits the acquired detection information to the learning device; a third acquiring unit acquires a model corresponding to the transmitted context information, from the learning device that determines whether any pieces of context information are identical or similar to each other and combines models generated from pieces of the detection information corresponding to the pieces of identical or similar context information; and a first determining unit determines whether an operation performed by the target device is normal by using the detection information and the model.