A gateway serving as a security apparatus connected to one or a plurality of buses includes a receiver that receives a frame from a bus, a parameter storage that stores an examination parameter defining a content of an examination of the frame, an updater configured to, in a case where a predetermined condition is satisfied for the frame received by the receiver, update the examination parameter stored in the parameter storage, and an examiner that performs an examination, based on the examination parameter stored in the parameter storage, in terms of judgment of whether or not the frame received by the receiver is an attack frame.