In a machine to be operated such that tools and a work are always brought into synchronism with each other, method and device for controlling at the time of power failure adapted to retract tools to a safe area without breaking the tools and a work at the time of power failure. When a power fails during synchronous operation (S1), a power supply regenerating operation in a power supply regenerating power circuit is halted (S2), sending to a motor for tools and a motor for a work, respectively, braking commands for controlling them to a reduced speed which is good enough to generate regenerating energy needed not only to keep a predetermined synchronism therebetween but also to drive a motor for moving tool shafts (S3), and driving the motor for moving tool shafts with regenerating energy produced through the speed reducing operation of the motor for tools and the motor for a work so as to retract the tools to an area where they do no interfere with the work (S4).