A coordinate measuring machine comprising a base provided with guides parallel to a first X axis, a first carriage mobile on the guides along the X axis and provided with an upright, a second carriage carried by the upright and mobile along a second vertical Z axis, and a horizontal-arm carried by the second carriage and axially mobile along a third horizontal Y axis perpendicular to the X axis; a counterweight, fastened to the second carriage by means of a belt, is mobile along the Z axis within the upright and is provided with wheels in contact with side walls of the upright.