Tensioning machine is special equipment for fabrication of middle and small concrete building block suitable for prestress jacking on cold drawn low carbon wires of ¢3.¢4.¢5 in long line bed box, with advantages of compactness, light in weight, easy for transport, correct in measurement of force, convenient for operation and maintenance. Spring is used for the measurement of force, the machine can be controlled automatically by means of prestress according to the preset jacking force.