To provide a durable valve timing adjusting device materializing valve timing adjustment suitable for an internal combustion engine.

The valve timing adjusting device 1 is provided with a magnetic viscous fluid 150 changing viscosity according to applied magnetic field, a rotor 130 applying brake torque according to viscosity of the magnetic viscous fluid 150 by touching the magnetic viscous fluid 150, a phase adjusting mechanism 8 adjusting relative phase between a crankshaft and a camshaft 2 according to brake torque input from the rotor 130, a solenoid coil 140 generating magnetic field applied to the magnetorheologcal fluid 150 by excitation, an excitation control circuit 160 variably controlling excitation current to the solenoid coil 140 during operation of the internal combustion engine and stopping excitation of the solenoid coil 140 during stop of the internal combustion engine, and a support body 110 forming a magnetizing part by a permanent magnet 144 and generating apply magnetic field to the magnetic viscous fluid 150.