To provide a positioning device by which the planer scanner is simplified, made small in size and the cost is reduced.

A table 5 of the planer scanner is provided with a placing face 51, a stopper 52 and a plurality of 1st holes 53 which act like a positioning device. The placing face 51 is made by processing horizontally an upper face of the table 5. Each of the 1st holes 53 is used to jet a gas delivered from a pump 7 onto a sensing member 11 so as to provide a propeling force having a floating force and a direction of the stopper 52 to the sensing member 11. The stopper 52 stops the sensing member 1 moving on the placing face 51 through the gas blowing as above.