Hydraulic trailer brake device

The unit has a trailer brake valve (20) to apply braking pressure, with a pressure connection (P) to a pump (2), a return connection (R) to a tank, and a brake connection (B). The valve is actuated dependent upon the brake pressure of a towing vehicle. An electronic control device (30) converts a pressure signal corresponding to that brake pressure, into an actuator signal to operate the trailer brake valve. This valve has an associated priority valve (24) for priority supply. It also has a device to calculate the trailer load and to issue a load signal to the electronic device, to alter the control signal correspondingly. When the trailer is uncoupled, the device issues a signal for automatic engagement of the trailer brake.