The present invention provides a device for generating and varying stiffness, which may be applied to a joint of a robot manipulator. The stiffness generating device of the present invention, comprises: a rotating shaft connected to a driven member; a rotor fixed to the rotating shaft and having arms comprising a magnetic element; a stator disposed to surround the rotor outside the arms and being connected to a drive motor; electromagnets fixed to an inner periphery of the stator and being opposed to each other about the rotating shaft, each having a core and a coil wound around the core; and means for applying current to the coils. One half of the electromagnets has N-poles at their inward ends and the other half of the electromagnets has S-poles at their inward ends. Current regulating means regulates the current being applied to the coils.