1. An offline programming device for preparing an operation program for making a robot with a hand attached thereto perform a handling operation for an object with respect to a machine tool, said object including at least one of a workpiece and a tool, the device comprising a computer having a processor configured to include: a hand-position designating section for designating a relative positional relationship between said object and said hand when said hand holds said object; a first calculating section for determining a position and orientation of said object mounted on said machine tool when said robot performs said handling operation, based on (i) a command specifying a position of said object and (ii) orientation data of a workpiece coordinate system provided in said machine tool, said command being included in a workpiece processing program given to said machine tool; a second calculating section for determining a position and orientation of said robot acting to hold said object by said hand when said robot performs said handling operation, based on (a) said relative positional relationship between said object and said hand designated by said hand-position designating section and (b) said position and orientation of said object determined by said first calculating section; an operation-program generating section for generating said operation program by using said position and orientation of said robot determined by said second calculating section; and an operation-program correcting section for (1) determining an error in a relative positional relationship between said machine tool and said robot, based on detection data of a position detector disposed adjacent to said hand of said robot, and (2) correcting said operation program in response to said error, when said operation program generated by said operation-program generating section is applied to a manufacturing system including said machine tool and said robot.