To easily, accurately, and numerically measure the thickness of a sheet, film, plate, etc., by using a dot printing means and an image reading means.

A thickness measuring instrument 100 incorporates a printing means 1 composed of a dot forming element, a printing head 2, a carriage 4, a printing-head drive control section 7, and object carrying means (51 and 52); an image sensor 3 which reads a thickness detecting pattern DP composed of a forward pattern DP1 and a backward pattern DP2 printed on an object 200 to be measured for thickness; and a thickness calculating means (pattern recognizing program PRprg) which calculates the thickness of the object 200 by analyzing the thickness detecting pattern DP read by means of the sensor 3. The instrument 100 also incorporates a display device 121 which outputs the results of thickness calculation by means of the thickness calculating means.