To provide a new synchronizing method and apparatus whereby, when the pseudo-random-pattern generating circuits having the mark ratio of 1/4, 1/8, or the like are synchronized with each other, their synchronization takes a short time independently of the period of a testing pattern.

In the synchronizing method and apparatus of the pseudo- random-pattern generating circuits having a variable mark ratio, the pseudo- random-pattern generating circuits are synchronized with each other by a step for setting them before their pull-in to the pseudo-random-pattern generating circuits having the mark ratio of 1/2, by a step for executing their pull-in in the state wherein they are set to the pseudo-random-pattern generating circuits having the mark ratio of 1/2, and by a step for returning them after their pull-in to the pseudo-random-pattern generating circuits having a predetermined mark ratio.