A platform assembly includes a first platform module having an elongated front face, a second platform module having an elongated front face, a locking member for locking the front faces of the first and second platform modules to each other when they are set against each other, which locking member is movably mounted on the first platform module. The locking member is mounted on the first platform module movably in the longitudinal direction of the front face of the first platform module, and at least one of the locking member and the second platform includes a locking protrusion protruding from the front face of the platform module, and the other of the locking member and the second platform includes a locking slot arranged to receive the locking protrusion when the front faces of the platform modules are set against each other, and an edge of the locking protrusion is arranged to move behind an edge of the locking slot when the locking member is moved in said longitudinal direction of the front face, thereby locking the platform modules to each other.