A digital trimming circuit is used to produce a stable time reference signal. This type of reference time signal can be used in equipment, such as watches, which have motors and acoustic outputs that interfere with producing the time reference signal. A basic oscillation frequency, which is produced by an oscillator circuit, is frequency divided to form the generic time reference signal. The digital trimming circuit generates a control signal to shorten the period of the time reference signal by predetermined amounts based on correction data. The control signal is in the form of pulses which can be dispersively applied to create substantially equal intervals between pulses during one time period of the time reference time signal. While maintaining the necessary digital trimming amount in one digital trimming time period, an expansion/reduction amount of the time reference signal is suppressed at one digital trimming time instant. Therefore, interference between the digital trimming timing and the predetermined output timing can be avoided.