Provided is a communication apparatus usable for any case where a time synchronization function is necessary or unnecessary by attaching or detaching a synchronization model for realizing the time synchronization function. A clock generation unit, a logic circuit unit including a synchronization module monitoring unit, a clock selection unit, and a main circuit unit configured by a switch LSI are integrally formed on the same substrate, and the synchronization module is detachably mounted on the substrate via connectors. The connectors each have a mounting determination pin that indicates a different signal level depending on whether the synchronization module is mounted. The synchronization module monitoring unit monitors connection signals indicating signal levels of the mounting determination pin, and causes the clock selection unit to select a synchronization clock when the synchronization module is mounted, and an internal clock when the synchronization module is not mounted.