A knee joint stimulation device comprising: a base ; a frame provided upright on the base ; a center shaft provided at an upper part of the frame ; a crank connecting a motor and the center shaft and driven by rotation of the motor , the center shaft being pivotable via the crank ; a swing arm hanging down perpendicularly from the center shaft or a pair of swing arms hanging down perpendicularly from both sides of the center shaft across the motor , a length of the swing arm or the swing arms being adjustable; and a support plate unit provided at a lower end of the swing arm or a pair of support plate units provided at lower ends of the pair of swing arms and allowing a user in a sitting position to put a sole or soles of the user thereon, wherein, with the user putting the sole or the soles on the support plate unit or the support plate units , the length of the swing arm or of the swing arms is adjusted such that a pivot point of a knee joint or pivot points of knee joints of the user is or are aligned with the center shaft , wherein, by swinging movement of the swing arm or swing arms , the support plate unit or the support plate units can move the sole or soles resting thereon in a flexion direction or an extension direction about the knee joint or knee joints , wherein the support plate unit is pivotable about a support shaft or the support plate units are pivotable about support shafts that horizontally extends or extend from the lower end or ends of the swing arm or swing arms , and wherein, even when the sole or soles resting on the support plate unit or units moves or move in a flexion direction or an extension direction about the knee joint or the knee joints and thereby the ankle joint is caused or the ankle joints are caused to move in a plantarflexion direction and a dorsiflexion direction, the support plate unit or the support plate units can pivotally follow the movement of the sole or the soles . a base ; a frame provided upright on the base ; a center shaft provided at an upper part of the frame ; a crank connecting a motor and the center shaft and driven by rotation of the motor , the center shaft being pivotable via the crank ; a swing arm hanging down perpendicularly from the center shaft or a pair of swing arms hanging down perpendicularly from both sides of the center shaft across the motor , a length of the swing arm or the swing arms being adjustable; and a support plate unit provided at a lower end of the swing arm or a pair of support plate units provided at lower ends of the pair of swing arms and allowing a user in a sitting position to put a sole or soles of the user thereon, wherein, with the user putting the sole or the soles on the support plate unit or the support plate units , the length of the swing arm or of the swing arms is adjusted such that a pivot point of a knee joint or pivot points of knee joints of the user is or are aligned with the center shaft , wherein, by swinging movement of the swing arm or swing arms , the support plate unit or the support plate units can move the sole or soles resting thereon in a flexion direction or an extension direction about the knee joint or knee joints , wherein the support plate unit is pivotable about a support shaft or the support plate units are pivotable about support shafts that horizontally extends or extend from the lower end or ends of the swing arm or swing arms , and wherein, even when the sole or soles resting on the support plate unit or units moves or move in a flexion direction or an extension direction about the knee joint or the knee joints and thereby the ankle joint is caused or the ankle joints are caused to move in a plantarflexion direction and a dorsiflexion direction, the support plate unit or the support plate units can pivotally follow the movement of the sole or the soles . <EOS>