A combustion-pressure-data acquisition system of a multi-cylinder engine according to the present invention includes an in-cylinder pressure sensor CPS#n for directly detecting combustion pressure in each cylinder; an amplifier unit AP#n to which the in-cylinder pressure sensor CPS#n for each cylinder is connected; and a channel switching unit MUX to which the amplifier unit AP#n for each cylinder is connected. It selects a system to be measured from among a plurality of systems of signals from the amplifier units AP#n with a channel selection signal outputted from an engine-controlling electronic control unit and outputs combustion pressure data to the ECU. Further, it outputs to an amplifier unit AP#n with which measurement ends a reset signal for discharging the electric charge between the in-cylinder pressure sensor CPS#n and the amplifier circuit to efficiently acquire combustion pressure data of each cylinder with a simple structure without complicated processing.