An instantaneous jitter information detection section detects, based on first and second digital values indicating different polarities relative to a predetermined reference value, an instantaneous gradient value corresponding to a difference value between the first and second digital values, and an instantaneous deviation value corresponding to a difference value between an intermediate value between the first and second digital values and the reference value. An information conversion section converts, based on an inversely proportional conversion table, the instantaneous gradient value to an inversely proportional value. An arithmetic section detects an instantaneous variance value by multiplying the instantaneous deviation value and the inversely proportional value together, and squaring a value obtained by the multiplication, and detects an integrated value by accumulating the instantaneous variance value. A standard deviation detection section detects a square root of a mean value of the integrated value as the absolute jitter value.