A reference signal generator generating a reference signal for high-resolution measurement/control in real time includes a means for calculating the rotational trend, e.g. increase/decrease in the r.p.m., of an engine when a first tooth is detected by an angle sensor at the (n-1)-th cycle according to the mutual relation between the time interval between the first tooth and a second tooth just before the first tooth at the (n-1)-th cycle of the engine rotation and the time interval between the first tooth and a third tooth just after the first tooth, a rotation time predicting means for predicting the time interval between the first tooth and the third tooth at the n-th cycle by reflecting the rotational trend on the time interval between the first tooth and the second tooth at the n-th cycle, and a means for generating a reference signal by dividing a predicted time interval in correspondence with a predetermined angle resolution during the time after the first tooth is detected by the angle sensor at the n-th cycle till the third tooth is detected by the same.