noise attendant upon ignition reaches a considerably high level therefore at the ignition timing the signal is masked so as not to receive the ignition noise thereby enabling a realiable detection of the signal from the knock sensor 1 in accordance with the embodiment described hereinabove by merely attaching the distributor to the block of the engine the mounting of the knock c u 44 of the knock control system is automatically completed and the wiring between the knock c u 44 and the igniter unit 43 is dispensed with the installation of the knock control system is effected by merely mounting the knock sensor 1 and carrying out the wiring therefrom the knock c u 44 thereby greatly simplifying the assembling process of the knock control system to the internal combustion engine as shown in fig9 and 10 it is possible for the knock c u 44 to be built into the igniter unit 43 with the ic unit generally being designated by the reference numeral 50 as shown in fig1 the ic unit 50 is fashioned so that ceramic ic substrates 502 503 are disposed on both surfaces of a metal plate 501 of for example copper or the like which serves both as a shield plate and a thermal diffusion plate with the ic unit 50 also including a power transistor 33 the ic substrate 502 and the power transistor 33 are connected by for example a wire bonding 504 in all other respects the embodiment of fig9 11 correspond to the embodiment described hereinabove in connection with fig4 and 5 with the exception of the differences relating to the specification of the distributor etc the ceramic ic substrate 502 bounded on one surface.