A rotary cylinder apparatus comprises a rotary drum mounted thereon with a magnetic head, a brushless motor for driving the rotary drum, a stationary drum housing the brushless motor and which is disposed opposing the rotary drum, and a revolution-rate detector for detecting the number of revolutions of the rotary drum. The brushless motor comprises a permanent magnet rotor connected to the rotary drum, a driving coil mounted on the stationary drum, and a position detector for detecting the position of the permanent magnet rotor in order to control current to be supplied to the driving coil. The detecting coil of the revolution-rate detector and the brushless motor are housed in the stationary drum and wiring of the driving coil and revolution-rate detecting coil is performed on a common wiring board. Thus, the driving section of the rotary cylinder apparatus is small-sized and made light in weight, and the number of processes of assembling the rotary cylinder apparatus can be decreased.