Provided are a relay device and the like with which it is possible to suppress bus signal reflections and suppress signal delays. A relay device 100A includes a signal processing and forwarding pathway P1 and a bypass connection pathway P2. The signal processing and forwarding pathway P1 processes a signal received from one bus CAN1 of a plurality of buses, and forwards the processed signal to another bus CAN2. The bypass connection pathway P2 connects the one bus CAN1 to the other bus CAN2, bypassing the signal processing and forwarding pathway P1.