To perform combined running according to the optimum diesel engine/ boiler load sharing without exceeding the value for environmental criteria of NOx.

In this device, an electric generation command 21 is inputted into a function generator 23. The function generator 23 determiners a load sharing function F1 to maximize a diesel engine load sharing based on the oxygen quantity required for a boiler and the oxygen quantity in the exhaust emission of a diesel engine. Denitration inlet NOx 22 is inputted into a function generator 24. The function generator 24 generates load sharing function F2 for the diesel engine and the boiler so that boiler outlet NOx does not exceed a reference value. Both of these functions F1 and F2 are multiplied by each other to determine the optimum, and the fuel quantity 27 to be inputted in the boiler and the fuel quantity 28 to be inputted in the diesel engine are calculated.