To continuously vary valve drive phase and valve lift quantity in simple constitution without causing reduction of valve overlap in a variable valve system in an internal combustion engine.

This device is provided with a rocker arm mechanism 10, 110 comprising a first arm supported by a rocker shaft 21, 121 to be capable of oscillating, a second arm driven by a cam to oscillate around a support point on the side of the rocker shaft 21, 121, a third arm provided on a support shaft to be capable of oscillating to be displaced by oscillation of the second arm to drive the first arm, and a variable mechanism to displace the support point of the second arm on the side of the rocker shaft 21, 121. A camshaft 20, 120, the rocker shaft 21, 121, and the rocker arm mechanism 10, 110 are respectively provided on the intake valve side and the exhaust valve side to be symmetric as seen from a crankshaft direction of the internal combustion engine. These are composed in such a way that rotation direction of the camshaft 20, 120 is the same on the intake valve side and on the exhaust valve side.