SOFTWARE UPDATE APPARATUS, SOFTWARE UPDATE METHOD, NON-TRANSITORY STORAGE MEDIUM STORING PROGRAM, VEHICLE, AND OTA MASTER

A software update apparatus (50) includes a communication unit (51) that sends a request for downloading update data to a center (100), a storage unit (53) that stores the downloaded update data, a control unit (52) that executes, based on the update data, a control for installing, or installing and activating update software on one or more target electronic control units from among a plurality of electronic control units (11, 12, 21, 22) connected to each other via an in-vehicle network, and a determination unit (54) that determines whether the vehicle is stopped and can be maintained in a stopped state. When a determination result of the determination unit (54) is positive, the control unit (52) restricts operations of the target electronic control units and executes the control for installing, or installing and activating.