Ignition controller for internal combustion engine

An ignition controller for an internal combustion engine provided with a slide-valve type carburetor (1) includes a throttle-position sensor (20) for determining the throttle position of a sliding throttle valve (6), and a control means (51) that controls ignition timing on the basis of the throttle position of the sliding throttle valve (6) according to a predetermined ignition timing characteristic having a predetermined first characteristic (A) and a predetermined second characteristic (B). The throttle-position sensor (20) is provided with a microswitch (40) and generates a specific signal when throttle position is on one side of a predetermined single boundary throttle position (N1) in a throttle-position range between a full-open throttle position and a full-closed throttle position. The control means (51) controls ignition timing on the basis of the first or the second characteristic depending on whether or not the specific signal is given. The throttle-position sensor of the ignition controller is simple in construction and can be manufactured at a low cost. The ignition controller ensures the specific performance of the internal combustion engine at low cost.