A variable valve mechanism includes an input arm that axially supports a roller pressed by a cam, via a roller pin, an output arm that drives a valve when swinging, a switch device that switches the variable valve mechanism between a coupled state where the both arms are coupled and an uncoupled state where the arms are uncoupled from each other, and a lost motion spring that biases the roller against the cam when in the uncoupled state. The lost motion spring includes an extended portion extending in an inter-arm clearance between the input arm and the output arm. An end of the roller pin projects from the input arm into the inter-arm clearance by such a length that the end is accommodated in the inter-arm clearance and that allows a spring retaining portion to be formed in the end. The spring retaining portion is formed in the end.