In the case where a temperature allowance of one translational mechanism of a plurality of the translational mechanisms (the electric motors 31R, 31L) larger than a temperature allowance of the other translational mechanisms, the operation mode of a plurality of the translational mechanisms are controlled so that the heat generation amount of the one translational mechanism becomes larger than the heat generation amount of the other translational mechanisms. By doing so, the difference between the temperature allowances of a plurality of the translational mechanisms is reduced.