An insulation displacement terminal of a high quality and high performance can be produced by designing the terminal in accordance with data measurement under a condition similar to an actual insulation displacement connection. An extent of insertion of an insulation sheath electric cable 6, a distance between a pair of metal blocks 11 and 12 spaced in parallel to each other, and a reaction force and a contact resistance acting between the cable 6 and the spaced metal blocks 11, 12 are measured, respectively, while inserting the cable 6 into a gap between the metal blocks 11 and 12 having a tapered portion on an end of each block. Then, an extent of insertion of the cable .DELTA.2, a gap distance WS2, a reaction force F2, and a contact resistance R2 after completing the insertion are obtained and at the same time an occurrence of broken wires in the cable is judged. These steps are repeated while changing an initial gap WS between the metal blocks 11 and 12. A range in which the contact resistance R2 after completing the insertion becomes stable and the breakage of wires is not caused is set to be an allowable range out of a variable range of the gap WS2 between the spaced metal blocks after completing the insertion in accordance with the data and at the same time the corresponding reaction force and extent of insertion after completing the insertion are set.