The present invention relates to a knee joint rehabilitation instrument. The knee joint rehabilitation instrument of the present invention includes a thigh fixing unit into which a thigh of a leg requiring rehabilitation is inserted and thereby fixed; a shin fixing unit which is disposed next to the thigh fixing unit and into which a shin of the leg requiring rehabilitation is inserted and thereby fixed; and a knee position guide which is disposed between the thigh fixing unit and the shin fixing unit and guides a position of a knee when inserting the leg requiring rehabilitation into the thigh fixing unit and the shin fixing unit.