A controller (70) controls the boost pressure of an internal combustion engine (60) comprising two intake/exhaust units, each intake/exhaust unit comprising a turbocharger (10) which supercharges intake air in an intake passage (20) using exhaust energy in an exhaust passage (30), and an exhaust gas recirculating device (40, 41) which recirculates a part of the exhaust gas in the exhaust passage to the intake passage. The controller (70) calculates an opening difference between valves in the two units (S121), and controls a regulating device (13) in each of the two units on the basis of this opening difference (S123-S125). As a result, the boost pressures of the turbochargers (10) match, and hence an equal amount of NOx can be discharged from each exhaust passage (30), and the NOx can be purified favorably by a catalyst.