PURPOSE: To prevent the occurrence of print deficiency by using a control system in which clock marks having different shapes of central, upper and lower parts are provided to a type belt and by the detection signals of the marks, skew is judged.

CONSTITUTION: In a printer in which types held on an endless belt are pressed on a recording paper through a printing paper and an ink ribbon by means of a hammer, clock marks 11 corresponding to types (a) provided on a type belt 6 are changed in terms of the shapes of the central part and the upper and lower parts. When the type belt 6 is running, the fixed position of the belt is controlled by detectung and judging the differences in wave form between clock pulse when the belt is turning at its fixed position and the clock pulse when the belt 6 is floated or settled by using the output of the clock marks 11 of a magnetic sensor.