To provide a control method for side trimming, capable of preventing the disorder of a shear plane at the side edge and obtaining a high quality metal steel band.

When the rotating speed of the upper round teeth 4a and the lower round teeth 4b of a trimmer 4 is slower with the change of the shape and component composition of a steel band 2, load is applied to a trimmer driving motor M1 to decrease a current value. In this case, a second adder/subtracter 26 computes a deviation between a trimmer driving current value ic1 and an actually measured current value ie1 to find a load current value iD for the trimmer driving motor M1. The load current value iD is input as a subtracted value to a third adder/subtracter 28, so that a value obtained by subtracting the load current value iD therefrom can be a baller correction driving curent value if2. When the rotating speed of the upper round teeth 4a and the lower round teeth 4b of the trimmer 4 is faster, load is applied to the trimmer driving motor M1 to increase a current value. In this case, a load current value iD as a negative value which is found by the second adder/subtracter 26 is input as a subtracted value into the third adder/subtracter 28, so that a value obtained by adding the load current value iD thereto can be a baller correction driving current value if2.