A new clamping machine is disclosed, which can perform a straight-hydraulic mold clamping and a tie-bar drawing-out operation in a reduced working space, and enables a shortened mold exchanging time, by effecting retraction of a movable die plate and a tie-bar drawing-out operation simultaneously. In order to draw out tie bars 18 from a fixed die plate 10 only when molds are exchanged, annular pistons 36, which construct mold clamping cylinders in the fixed die plate, are provided. Abutting each piston, a pair of half nuts 48A, 48B are arranged and driven to engage with an engagement portion 18A provided at one end of each tie bar on the side of the fixed die plate, usually, other than during the drawing out operation. A relative position of each tie bar to the half nuts is set to be able to engage with the half nuts when a right end face of the tie bar contacts with the stopper plate 46. When pressure for clamping molds is increased during such engagement, the annular pistons are driven to transmit a force, for performing an initial operation, to the tie bars.