A manipulator operative in a master/slave operative mode includes a master unit commanding an operation; a slave unit having a work unit; a detector detecting the orientation of the master unit and the orientation of the slave unit; and a control device controlling the slave unit in response to a command from the master unit. The control device determines a non-master/slave operative mode or a master/slave operative mode, and calculates a difference between the orientation of the master unit and the orientation of the slave unit. The absolute value of the calculated difference is compared with a preset reference value, and depending upon the result of the comparison, a normal master/slave operative mode or a transitional master/slave operative mode is determined, wherein in the master/slave operative mode, the transitional master/slave operative mode is a transitional mode from the non-master/slave operative mode to the master/slave operative mode.