PURPOSE: To realize a compact mold clamping unit and injection unit by a method wherein a mold clamping space is made between a stationary platen and a moving block and mold clamping mechanism is provided between the moving block and a rear platen.

CONSTITUTION: A moving block 8 is installed movably to and fro in a box type first casing 5 between a stationary platen 6 and a rear platen 14. Further, a mold clamping space 19 is made between the stationary platen 6 and the moving block 8 and, at the same time, mold clamping mechanism 20 is provided between the moving block 8 and the rear platen 14. The above-mentioned structure forms a mold clamping unit. Thus, an injection unit is assembled within the mold clamping unit structure, resulting in forming a compact motorized injection molder as a whole.