An improved linear guiding mechanism with a standing part and a moving part which have respective uniform cross sections. A pair of spaced guiding channels is formed between these parts and respective linear ball bearings are arranged in both channels that interconnect the two parts. The channel walls are abutting the balls via steel bars extending along the channels. Preferably the standing part defines a cylinder in which a piston is moved and its shaft is connected to the moving part. The parts are made of light and soft material such as aluminum or plastic and manufactured by extrusion technique. The rather high variation of dimensions of such parts are compensated by means of biasing forces that press the channels together, and the biasing forces are sufficiently high to resist operational load. The length of the ball bearings is at least the half of the maximum stroke.