PURPOSE: To enable motion to be changed at an optional point in a cylinder stroke by attaching electromagnetic sensors on a cylinder outer part, and feeding positional information of the cylinder back into a calculating device.

CONSTITUTION: Solenoid valves 11 to 14 and flow rate valves 21, 22 are connected to a cylinder 1. Variable pressure valves 31, 32 are connected to a pressure reserving tank 4 and a high-pressure reserving tank 5, and output from the high-pressure reserving tank 5 is divided into two, and flow rate valves 23, 24 are connected to the two devided outputs, and the flow rate valves are connected to each other midway between the solenoid valves 11, 12, and 13, 14. Moreover, flow rate stepping motors 41, 42, 45, 46 are connected to one another, and invertor motors 43, 44 are connected to the variable pressure valves. The optional number of solenoid sensors 51 to 54 are attached to the cylinder outer part on both ends of the cylinder stroke and on the optional positions between the ends, and a calculating device for processing and controlling information of respective electromagnetic sensors 51 to 54 is attached.