It is an object to provide an engine that makes it possible to constantly detect the number of rotations of a supercharger with a calculation load of an ECU reduced. An engine 1 is provided with an engine base 8 comprised of a plurality of cylinders and a turbocharger 7, a crank angle sensor 4, a turbo sensor 5 that detects rotations of the turbocharger 7 as pulses, an amplifier 11 that divides the pulses by an arbitrary division ratio and calculates the divided pulses, and an ECU 10 that judges a surge condition of the turbocharger 7, wherein the ECU 10 sets a predetermined position of a piston of each cylinder in a crank angle of the engine base 8 to count start timing of the divided pulses, outputs the divided pulses counted from the count start timing to the number of predetermined rotations as a first output, and judges that, if a difference between the first outputs at every cylinder is more than a predetermined value, the turbocharger 7 is in the surge condition.