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

A software update apparatus includes a communication unit that sends a request for downloading update data to a center, a storage unit that stores the downloaded update data, a control unit 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 connected to each other via an in-vehicle network, and a determination unit that determines whether the vehicle is stopped and can be maintained in a stopped state. When a determination result of the determination unit is positive, the control unit restricts operations of the target electronic control units and executes the control for installing, or installing and activating.