PURPOSE: To set the starting point of information processing with accuracy by detecting that a rotary type information recording device attains a steady number of revolution after the device started.

CONSTITUTION: When the starting setting operation of an information processor 1 is carried out by an input device 7, a control part 4 starts the information recording device 1. The information recording device allows a disk, etc., to rotate and once its number of revolution attains a specified value or more, one pulse signal is outputted on every turn and supplied to and counted by a counter 2. When its counted value attains a prescribed value, a signal is outputted to set a flip-flop circuit 3 to output the set signal. Its set signal is a detection signal for attaining the steady number of revolution and transmitted to the control part 4, which displays the processing in readiness on a CRT5 or printer 6.