The present disclosure relates to an accessory detachably coupled to an electronic device, the electronic device, and a method of processing an input in the electronic device. The accessory includes a body part located on at least one surface of the electronic device when the accessory is attached to the electronic device, an opening into which a part of a pen is inserted, a depression into which a pen point of the pen is inserted, and a pen accommodation part that comprises a lateral portion located between the opening and the depression and a cavity located below the lateral portion to allow the pen to move when inserted, where the body part is formed of a magnetic material so as to be attached to and detached from the electronic device, and where the cavity contains a conductive material through which a signal generated from the pen when inserted into the depression is transferred to a touch panel of the electronic device.