An electronic key for a vehicle includes an upper case component of a key case, a lower case component attachable to the upper case component, and a mechanical key that is selected from among a first mechanical key that is used in a state of being totally removed from the key case and a second mechanical key that is used in a protruding state of partially protruding from the key case. The lower case component is selected, so as to correspond to the mechanical key, from among a first lower case component that accommodates the first mechanical key to be removable and a second lower case component that accommodates the second mechanical key to be movable into the protruding state.