This paper proposes a simulator that can depict the rotational vibration of a spur gear having any types of tooth surface deviation including both tooth profile deviations and tooth helix deviations. The developed simulator is based on a single degree-of-freedom model consisted of equivalent mass, damping and mesh stiffness of a gear pair. The mesh stiffness is calculated by considering the effect of the tooth helix deviation which brings non-uniform load distribution along the contact line of the tooth pair. The dynamic load tests have been performed to verify the simulator changing both helix slope deviations of the driven gear and torque. The analytical result under each operating condition is in good agreement with the experimental result. Moreover, the damping ratio of the test gear system is evaluated as 0.03 with the measured vibration responses, which is less than conventional expectation value of 0.07.