To prevent it from becoming longer than reference chopping timing, and prevent the noise in an electric motor.

This controller generates an ascending order saw-tooth wave signal S5 and a binary signal S6 to generate the reference chopping timing, synchronized with this ascending order saw-tooth wave signal, by an ascending order saw-wave generating circuit 11, inverts the ascending order saw-tooth wave signal S5, adds a descending saw-tooth wave signal S7 to a reference current signal S3, and generates a binary signal S9 by the comparison between the additional signal S8 and an actual current signal S1. Moreover, this generates a signal S11 which gets on low level L each time the signal S9 starts up and gets on high level each time it comes to take reference chopping timing by a flip flop 17, and this inputs a binary signal S4 which gets on high level H during the current application to the coil 1 and the signal S9 into an AND gate 15, and inputs the output signal S10 and a signal S11 into an AND gate 18 so as to generate a signal S12, and then this generates a signal S13 to operate a switching element 4 by this signal S12 and the reference chopping timing signal S6.