An oscillator with a noise reduction function is provided that can arbitrarily change the setting of a spread spectrum modulation and easily reduce the noise of electronic equipment, a writing device that can change the setting of the oscillator, and a control method of the writing device. The oscillator (10) has a memory (80) that stores modulation data (DM) for performing the spread spectrum modulation input from an output terminal (fout), a modulation signal output circuit (60) that generates a modulation signal (SM) from the modulation data (DM) stored in the memory (80), and a mixer (53) that superimposes the modulation signal (SM) on the control voltage (VC) of a voltage control oscillator (VCO) (54) of a PLL circuit (50); by these means it becomes possible to output a spread spectrum modulated output signal (CLv) under a specification desired by a user by storing in the memory (80) the modulation data (DM) that corresponds to the spread spectrum modulation the user tries to set.