To install a special purpose hydraulic apparatus without necessity of man power by pivotally securing two hydraulic cylinders for forwarding and reversing an injection unit to right and left positions of a stationary platen of an injection molding machine, pivotally securing rods of the cylinders to the injection unit mounted on a swivel base, and synchronously reversely operating the two cylinders.

When hydraulic cylinders 6 of an operating side and non- operating side are synchronously reversely operated in such a manner that the cylinder 6 of the operating side is projected and the cylinder of the non- operating side is returned, degrees of freedoms are given to the cylinders 6 in a horizontal direction, a rotary force is generated, and an injection unit 3 is swivelled at a swivel pin 5 as a center. That is, the unit 3 mounted on a swivel base is conducted in forward and reverse operations and swivelling operation by the two cylinders 6 provided at right and left positions of a stationary platen 7 of an injection molding machine.