PURPOSE: To automatically set a detecting condition by converting the detecting condition of paper thickness or the like into voltage applied to a cantilever- shaped variable contact member formed of a laminated actuator, so that a space between the variable contact member and a roller arm detecting contact can be changed.

CONSTITUTION: A supporting bracket 18, which is the base unit of a device, is secured to a supporting shaft 17, and an L-shaped roller arm 20 is pivotally supported to a supporting point 19 provided in a point end of this supporting bracket 18, to rotatably support a detecting roller 22 opposed to a feed roller 21 by interposing paper 23, which is a detecting object, in a point end of this arm 20. At the time of setting a detecting condition of thickness or the like of the paper 23, by converting the detecting condition into a voltage value applied to a variably setting member 27 formed of a laminated piezoelectric actuator, this member 27 is deflection deformed, to change a space between a detecting contact 24 of the roller arm 20 and a detecting contact 28 of the variable contact member 27. In the case of generating a double-sheet insert, by closing both the detecting contacts 24, 28, abnormality is detected as an electric signal.