In a camshaft adjusting device for adjusting a phase position of a camshaft, including a rotary actuator having a stator and at least one axially displaceable rotor and including a gear mechanism which is arranged operatively between two of at least three shafts, one of the shafts being a control shaft which is acted upon by the rotary actuator, one of the shafts being a drive shaft which is connected to the crankshaft, and one of the shafts being an output shaft which is connected to the camshaft, a compact locking structure is provided whereby at least two of the at least three shafts can be locked to one another in a rotationally fixed manner by a spring depending on operating conditions and released by an auxiliary coil which, upon energization, provides for axial movement of the rotor out of its locked position to permit adjustment thereof.