To aim provide a software update apparatus including an install module group (130) composed of a plurality of install modules. Each of the install modules has a function of receiving, from an external server (200), a replacement protection control module (121) to be used for updating a protection control module (120) having a function of verifying whether a predetermined application has been tampered with. Each of the install modules simultaneously running is verified by at least another one of the install modules simultaneously running, as to whether the install module has a possibility of performing malicious operations. If any of the install modules is verified as having the possibility of performing the malicious operations, any another one of the install modules that is verified as not having the possibility revokes the any install module verified as having the possibility.