To perform centering operation to make the distal end of an endoscope linear with respect to its insertion portion even at narrow space and to complete the centering operation with one operation without contact of the distal end of the endoscope with the circumference.

The remaining angles of bending in U/D directions and L/R directions are calculated by the values at which the amounts of U/D potentiometer 9 and L/R potentiometer 11 by an analog-to-digital converter 14 within a control circuit 12 upon receipt of a centering instruction. The control circuit 12 carries out the bending operation reverse from a direction where the remaining angle of bending exists, I.e., downward in the case of the state that the bending is applied upward just before, for example, a centering switch 19 is operated and bended rightward in the case of the state that the bending is applied leftward just before the centering switch 19 is operated. Then the bending angle is made zero.