A diagnosis device includes: a processor that executes a diagnosis program; and a memory that stores the diagnosis program, wherein the processor, based on the diagnosis program, performs operations to: collect a data transmission variable set by a data transmission path characteristics from a transceiver device on a diagnosis target path; and perform diagnosis for the diagnosis target path with reference to diagnosis reference information that includes a value of the data transmission variable and determination information associated with each other, based on collected data transmission variable.