A robot system comprising: a changeable robot mechanism section; a robot control section for controlling respective axes of said robot mechanism section, said robot mechanism section comprising motors (11, 12) for driving the respective axes; and a memory provided at said robot mechanism section, and configured to store information concerning parameters inherent to individuality of said robot mechanism section, said memory being connected with said robot control section so that the stored information is read by said robot control section, wherein said memory is configured to store identification information for identifying individuality of the robot mechanism section, and said robot control section is configured to read the identification information from said memory, such that, if the read identification information is different from corresponding identification information stored in the robot control section, the read information including the identification information replaces the corresponding information stored in the robot control section, such that the read information is used in calculation for a locus control of the robot mechanism section by said robot control section, characterised in that: said robot mechanism section comprises one or more encoders (13, 14) for detecting rotational positions of the motors (11, 12); said memory comprises a nonvolatile memory (13, 14) associated with one of said encoders (13, 14); and said robot control section is configured to read information stored in the nonvolatile memory (13, 14) using a communication line (3, 31) between said one of the encoders (13,14) and said robot control section. a changeable robot mechanism section; a robot control section for controlling respective axes of said robot mechanism section, said robot mechanism section comprising motors (11, 12) for driving the respective axes; and a memory provided at said robot mechanism section, and configured to store information concerning parameters inherent to individuality of said robot mechanism section, said memory being connected with said robot control section so that the stored information is read by said robot control section, wherein said memory is configured to store identification information for identifying individuality of the robot mechanism section, and said robot control section is configured to read the identification information from said memory, such that, if the read identification information is different from corresponding identification information stored in the robot control section, the read information including the identification information replaces the corresponding information stored in the robot control section, such that the read information is used in calculation for a locus control of the robot mechanism section by said robot control section, characterised in that: said robot mechanism section comprises one or more encoders (13, 14) for detecting rotational positions of the motors (11, 12); said memory comprises a nonvolatile memory (13, 14) associated with one of said encoders (13, 14); and said robot control section is configured to read information stored in the nonvolatile memory (13, 14) using a communication line (3, 31) between said one of the encoders (13,14) and said robot control section. said robot mechanism section comprises one or more encoders (13, 14) for detecting rotational positions of the motors (11, 12); said memory comprises a nonvolatile memory (13, 14) associated with one of said encoders (13, 14); and said robot control section is configured to read information stored in the nonvolatile memory (13, 14) using a communication line (3, 31) between said one of the encoders (13,14) and said robot control section.