To provide an ignition timing control device suppressing an insufficient lag amount when one of ignition plugs fail while suppressing an amount of ignition timing shifted from MBT (minimum advance for best torque).

This control device is provided with a basic ignition timing setting means for setting basic ignition timing, a lag correcting means for correcting the basic ignition timing to be lagged when knocking occurs, a maximum lag amount setting means for setting a maximum lag amount being the upper limit of a correction amount, and a failure detecting means for detecting whether or not one-sided failure occurs (S200). When the one-sided failure is detected, the maximum lag amount setting means sets the maximum lag amount to a value (S220) larger than a case where the one-sided failure is not detected.