A position detecting device, including: a movable section which has an axial section and moves in a direction of an axial line of the axial section; and a supporting section which supports the movable section and allows the movable section to move through the axial section; wherein the movable section includes a basic position section which is arranged on a virtual surface which includes the axial line of the axial section, and the virtual surface is vertically positioned on the supporting section toward the axial section, wherein the supporting section includes a position detecting section to detect a positional change of the basic position section; and wherein the position detecting device detects the position of the movable section relative to the supporting section, based on the change of position of the basic position section, detected by the position detecting section.