An optical driving device and an optical communication system are provided which can improve signal quality of laser light that uses a PAM method. A laser driver drives a semiconductor laser by usingan N-level (N is an integer of 3 or more) PAM signal. A clock control circuit determines a driving timing of the laser driver. In a case where N=4, for example, the clock control circuit determines adriving timing in association with a transition of the PAM signal from a fourth level to a first level to be earlier than a driving timing in association with a transition in an opposite direction bya first time, assuming that levels are the first level, . . . , and the fourth level in an order from a level at which light intensity is minimum.