A valve train of a combustion piston engine having an actuating device which comprises a phase shift gearbox with two inputs and an output for phase adjustment of a camshaft. The first input is connected with a crankshaft, the second input is connected with a controllable braking device and the output is rotationally fixed with the camshaft. The brake is an electromagnetically controlled friction brake which comprises an electromagnet and magnetic coil. A brake rotor is connected with the second input and can be biased, by the magnetic field of the electromagnet, against a friction surface. A permanent magnet is positioned axially adjacent the brake rotor such that, by its magnetic field, the brake rotor can be pressed against a fixed friction surface for the adjustment of a basic brake torque with the respective basic pressing force.