Locking device and knobless armrest assembly including the same

The locking device includes a cam member rotatable about a second axis parallel to a first axis and a rotator for transmitting rotational force of an armrest to the cam member in a contact manner to control rotation of the cam member. When the armrest is rotated, the rotator is rotated about the first axis, and a locking tooth of the rotator is moved so as to pass through a locking position. The cam member is rotated in accordance with control operation of rotation of the rotator, and a locking recess in the cam member is moved so as to pass through the locking position. When the armrest is rotated to assume a locking posture, the locking tooth and the locking recess are moved to the locking position, and the locking tooth is inserted into the locking recess.