The invention discloses a digital position instruction signal modification device for use with a memory controlled manipulator apparatus of the type in which, during a teaching operation, a desired position of manipulator arm means is stored in memory means, and the stored position is read out during repetitive work cycles to cause the manipulator apparatus to reproduce a series of motions taught during the teaching operation. The digital position instruction or command read out from the memory means may be modified by a modifying value entered by a modifying value setting device so that all or desired digital position command or instruction signals stored in the memory means may be modified without repeating the teaching operation.