According to an embodiment, a digitally controlled oscillator outputs an oscillation signal having an oscillation frequency according to an oscillator tuning word. The digitally controlled oscillator includes a control unit and an oscillator. The control unit divides the oscillator tuning word of N bits into upper (N−A) (A≧1 and N>A) bits and lower A bits, converts the upper (N−A) bits into a first code to perform Binary control of (N−A) bits and converts the lower A bits into a second code to perform Unary control of (2^(A+1)−2) bits, and outputs the conversion results, and the oscillator outputs oscillation signals having oscillation frequencies according to the first and second codes output from the control unit.