An offline teaching device comprising: a control unit having a selection function, a first change function, and a second change function; a welding line storage unit that is connected to the control unit, and having a welding line storage function; and a teaching program storage unit that is connected to the control unit, and having a teaching program storage function, wherein the welding line storage function stores a plurality of welding lines which have a plurality of coordinate positions in a welding path and a welding condition which is information relating to welding in each of the coordinate positions, and welding line identification information is assigned to each of the plurality of welding lines, the teaching program storage function stores a teaching program having a plurality of instructions to which the welding line identification information is assigned, and having the welding condition, the selection function causes one welding line among the plurality of welding lines stored in the welding line storage function to be selected, the first change function causes content of the welding condition configuring the welding line selected with the selection function to be changed, and the second change function causes the welding condition of the entirety of instructions in the teaching program having the same welding line identification information as the welding line identification information that is assigned to the welding line selected with the selection function to be changed to the same content as content changed with the first change function, characterized in that a welding condition identification information is assigned to the welding conditions, and in that the second change function further applies the same welding conditions to different welding lines by assigning the same welding condition identification information to welding line to which different welding line identification information is assigned in teaching program. a control unit having a selection function, a first change function, and a second change function; a welding line storage unit that is connected to the control unit, and having a welding line storage function; and a teaching program storage unit that is connected to the control unit, and having a teaching program storage function, wherein the welding line storage function stores a plurality of welding lines which have a plurality of coordinate positions in a welding path and a welding condition which is information relating to welding in each of the coordinate positions, and welding line identification information is assigned to each of the plurality of welding lines, the teaching program storage function stores a teaching program having a plurality of instructions to which the welding line identification information is assigned, and having the welding condition, the selection function causes one welding line among the plurality of welding lines stored in the welding line storage function to be selected, the first change function causes content of the welding condition configuring the welding line selected with the selection function to be changed, and the second change function causes the welding condition of the entirety of instructions in the teaching program having the same welding line identification information as the welding line identification information that is assigned to the welding line selected with the selection function to be changed to the same content as content changed with the first change function, characterized in that a welding condition identification information is assigned to the welding conditions, and in that the second change function further applies the same welding conditions to different welding lines by assigning the same welding condition identification information to welding line to which different welding line identification information is assigned in teaching program.