A heat exchanger includes a shell communicating with a first fluid inlet pipe and a first fluid outlet pipe, end caps coupled to ends of the shell to communicate with a second fluid inlet pipe and a second fluid outlet pipe, a plurality of tubes disposed in the shell to constitute a channel through which a second fluid flows, an end baffle located at ends of the tubes to prevent mixing of a first fluid and the second fluid, and a first plate to fill gaps between the tubes and the end baffle.