An ignition device, including: an
ignition coil (1) having a primary coil and a secondary coil; a switching element (5) for causing a primary current to be conducted through and shut off from the primary coil of the
ignition coil; a
waveform shaping circuit (6) for shaping a waveform of an ignition
signal transmitted from an outside through a
signal line to supply a conduction
signal thus obtained to the switching element;
ion current detecting means (8, 9) connected to the secondary coil of the
ignition coil, for detecting an
ion current flowing through the secondary coil; and
ion signal generating means (10, 11, 12) for outputting an ion signal, which indicates the
ion current detected for a predetermined period after the conduction signal of the
waveform shaping circuit has been turned off, to the outside through the signal line while invalidating the conduction signal from the
waveform shaping circuit.