An external accessory that can be attached to and detached from an electronic apparatus equipped with a power source unit includes: a first power receiving unit that receives power from the power source unit of the electronic apparatus; a second power receiving unit that receives power from the power source unit of the electronic apparatus; a decision-making unit that makes a decision as to whether or not the first power receiving unit is receiving power; a function execution unit that executes a predetermined function by using power received at one of the first power receiving unit and the second power receiving unit; and a control unit that engages the function execution unit in operation continuously when an affirmative decision is made by the decision-making unit, and engages the function execution unit in operation intermittently when a negative decision is made by the decision-making unit.