An external locking device is mounted on a holder. An operation member of the holder is moved between a first position where the operation member is substantially flush with an exterior of the holder and a second position where the operation member protrudes from the exterior. A first electronic device is detached from the holder when the operation member moved to the second position. The external locking device includes a locking member, a shaft member that rotates to a locking position during locking of the locking member and rotates to an unlocking position during unlocking of the locking member, and a moving member. When the shaft member is located at the locking position, the moving member moves to a space where the operation member is to be located at the second position. When the shaft member is located at the unlocking position, the moving member retreats from the space.