A form measuring instrument includes: a contact tip configured to contact with a workpiece; a movement mechanism configured to cause relative movement of the contact tip with respect to the workpiece; a movement controlling unit configured to control the movement mechanism; a contact sensor configured to detect a contact amount of the contact tip with the workpiece and output a detection signal corresponding to the contact amount; and an abnormality determining unit configured to determine an abnormality of sensitivity of the contact sensor based on a change in the detection signal outputted from the contact sensor during an operation of the movement mechanism in which the contact tip is pressed against the workpiece.