A printer includes a board configured to control a printing unit operating in the printer that performs printing on a medium, and a heat sink including a counter surface that is provided to face a board surface of the board and that has a shape with a length in a first direction X longer than a length in a second direction Y intersecting the first direction X in a plan view, and configured to receive heat generated in the board with the counter surface and dissipate the heat to the outside. The counter surface includes a slit penetrating the counter surface and extending in the second direction Y.