A digital system that performs a specified function by performing digital processing according to one or more clock signals is provided with a plurality of delay elements which are respectively inserted in a plurality of clock circuits that supply the clock signals in the digital system and each of which is composed of a circuit element that changes a delay time according to a value indicated by a control signal, and a plurality of holding circuits that hold a plurality of control signals to be given to the plurality of delay elements. In the plurality of holding circuits, a value of the control signals held by these holding circuits is changed by external devices according to a probabilistic search technique so that the digital system operates correctly in relation to operation timing.