Disclosed is a variable valve mechanism 10 for changing the lift amount and operating angle of an internal combustion engine valve disc 12. The variable valve mechanism comprises a first cam 54, which rotates in accordance with crankshaft rotation; a transmission member 24, 38 that includes a second cam 32, 34, which oscillates in synchronism with the rotation of the first cam 54 and transmits the force exerted by the first cam 54 to the valve disc 12; a control shaft 40, which is adjusted for a predetermined rotation position; an adjustment mechanism 36, 38 for varying the lift amount and operating angle of the valve disc 12 by changing the oscillation range of the transmission member 24, 38 in accordance with the rotation position of the control shaft 40; a lost motion spring 60 for pressing the transmission member 24, 38 toward the first cam 54 to ensure that the transmission member 24, 38 remains coupled to the first cam 54; and an assist spring 64 for pressing the transmission member 24, 38 in resistance to the force exerted by the lost motion spring 60.