A ring binder mechanism has at least two semi-ring pairs, which are arranged spaced apart from one another and which each consist of two semi-rings (20, 20′), the semi-rings (20) of a first group and the semi-rings (20′) of a second group being rigidly connected to one another in a grouped manner in the area of their roots and thereby kept spaced apart from one another. Mutually complementary locking bar elements (44, 44′), which, in the closed position, are locked to prevent pivoting of the semi-rings relative to one another, are arranged at the ends of the semi-rings (20, 20′) of at least one of the semi-ring pairs. In a free position, the semi-rings (20, 20′) allocated in pairs span a common radial plane (46), and the locking bar elements (44, 44′) thereof are spaced radially apart from one another, and in the locked position, the locking bar elements (44, 44′) are coupled to one another with a form fit in all directions within the tangential plane (48) of the rings (19) which intersects the locking bar elements (44, 44′) and is perpendicular to the radial plane (46).