An anti-lock/traction modulator which includes a hydraulic pressure passage circuit for an anti-skid control and a hydraulic pressure source circuit for a traction control in which an accumulator disposed at an inlet side of a pump for accumulating a predetermined pressure and which circuit supplies a brake pressure to the hydraulic circuit for the anti-skid control merely during the traction control operation. These circuits are connected to each other through a piston so that brake pressure is supplied to brake cylinders of vehicle wheels from the piston during the traction control operation.