To compress the memorizing capacity of a memory and simultaneously shorten a time for reading the memorized data on the opening pattern of an opening frame.

In this motor-driven opening device 1 of such a type that each opening frame 2 is independently driven synchronously with the rotation of the main shaft 7 of a loom, the constituting factors of the opening movements are preliminarily set, and the constituting factors are selected for each opening step. A command for the opening degree of the opening frame 2 in response to the rotation of the main shaft 7 on the basis of an opening curve comprising the selected constituting factors is outputted to drive the opening frame 2.