A coordinate measuring machine (1) comprising a base (2) provided with guides (3) parallel ● to a first axis X, a first carriage (4) mobile on the guides (3) along the axis X and provided with an upright (17), a second carriage (6) carried by the upright (17) and mobile along a second vertical axis Z, and a horizontal arm (7) carried by the second carriage (6) and mobile along a third horizontal axis Y perpendicular to the axis X; the guides (3) of the first carriage (4) are arranged underneath a top wall (12) of the base (2), which is therefore flat and treadable.