A camera apparatus and a camera system of the present invention are configured so that a lens unit is attachable/detachable. The lens unit contains at least a lens and an iris, and contains a memory storing setting information required for operating the lens and the iris. When a camera microcomputer checks detection information stored in a memory in a sub-microcomputer at a time of start-up of the camera apparatus, and first detection information is stored in the memory, the setting information is acquired from the lens unit. When second detection information is stored in the memory, the setting information is acquired from another memory in the camera apparatus. Due to this configuration, the time for shifting the switch-on to a photographable state is shortened, and the ease of convenience can be enhanced.