An operation device, comprising: an operation inputter (311, 381) for operating a robot, the robot comprising a leading end and a multi-articular arm configured to change a position and a posture of the leading end; a device posture detector (321, 382) configured to detect a posture of the operation inputter (311, 381) in a first coordinate system that is associated to the robot and is for controlling the robot; the operation device being characterized by further comprising: a coordinate system turner configured to, based on the posture of the operation inputter (311, 381), turn a second coordinate system associated to the operation inputter relative to the first coordinate system based on the posture of the operation inputter, wherein the turning angle of the second coordinate system relative to the first coordinate system is defined based on an initial posture in which the X axis, the Y axis, and the Z axis of the first coordinate system respectively coincide with the X axis, the Y axis, and the Z axis of the second coordinate system; a command generator configured to, based on an input operation made by an operator into the operation inputter (311, 381) in the turned second coordinate system, generate a motion command for the leading end of the robot in the turned second coordinate system; a command convertor configured to convert the motion command into a first-coordinate-system motion command for the leading end of the robot in the first coordinate system; a command outputter configured to output a control command for controlling the robot based on the first-coordinate-system motion command; and a coordinate system turning regulator configured to regulate the turning of the second coordinate system such that the turning is prohibited about at least one axis. an operation inputter (311, 381) for operating a robot, the robot comprising a leading end and a multi-articular arm configured to change a position and a posture of the leading end; a device posture detector (321, 382) configured to detect a posture of the operation inputter (311, 381) in a first coordinate system that is associated to the robot and is for controlling the robot; the operation device being characterized by further comprising: a coordinate system turner configured to, based on the posture of the operation inputter (311, 381), turn a second coordinate system associated to the operation inputter relative to the first coordinate system based on the posture of the operation inputter, wherein the turning angle of the second coordinate system relative to the first coordinate system is defined based on an initial posture in which the X axis, the Y axis, and the Z axis of the first coordinate system respectively coincide with the X axis, the Y axis, and the Z axis of the second coordinate system; a command generator configured to, based on an input operation made by an operator into the operation inputter (311, 381) in the turned second coordinate system, generate a motion command for the leading end of the robot in the turned second coordinate system; a command convertor configured to convert the motion command into a first-coordinate-system motion command for the leading end of the robot in the first coordinate system; a command outputter configured to output a control command for controlling the robot based on the first-coordinate-system motion command; and a coordinate system turning regulator configured to regulate the turning of the second coordinate system such that the turning is prohibited about at least one axis. a coordinate system turner configured to, based on the posture of the operation inputter (311, 381), turn a second coordinate system associated to the operation inputter relative to the first coordinate system based on the posture of the operation inputter, wherein the turning angle of the second coordinate system relative to the first coordinate system is defined based on an initial posture in which the X axis, the Y axis, and the Z axis of the first coordinate system respectively coincide with the X axis, the Y axis, and the Z axis of the second coordinate system; a command generator configured to, based on an input operation made by an operator into the operation inputter (311, 381) in the turned second coordinate system, generate a motion command for the leading end of the robot in the turned second coordinate system; a command convertor configured to convert the motion command into a first-coordinate-system motion command for the leading end of the robot in the first coordinate system; a command outputter configured to output a control command for controlling the robot based on the first-coordinate-system motion command; and a coordinate system turning regulator configured to regulate the turning of the second coordinate system such that the turning is prohibited about at least one axis.