An electrical swivel working machine includes a lower-part traveling body; an upper-part swivelling body mounted on the lower-part traveling body so as to be rotatable relative to the lower-part traveling body; a swivel mechanism supporting the upper-part swivelling body so that the upper-part swivelling body is rotatable relative to the lower-part traveling body; a motor for sniveling the upper-part swivelling body relative to the lower-part traveling body as a drive source of the swivel mechanism; and a swivel control part generating a drive command for driving the motor, wherein the swivel control part performs a slip prevention mode where a swivel operation of the upper-part swivelling body is mild relative to an ordinary swivel mode.