An interference determination method of determining whether it is possible that a robot including a plurality of movable shafts interferes with a surrounding object that exists around the robot while the robot moves from a first position to a second position, using a computation device including an acquisition unit, a storage unit, and a computation unit, wherein the computation unit executes: storing robot data for approximating a shape of the robot as a polyhedron for each of a plurality of movable parts (L1-L5) of the robot into the storage unit; storing data of a surrounding object approximated body that approximates the shape of the surrounding object into the storage unit, wherein the surrounding object approximated body is a first cuboid, a first cuboid being a type of cuboid constituted by line segments that are parallel to respective axes of an absolute reference coordinate system constituted by three axes that are orthogonal to each other; acquiring the first position and the second position using the acquisition unit; setting at least one intermediate position (M1-M7) on a motion path of movement from the first position to the second position; generating a plurality of robot approximated bodies that approximate the shape of at least one movable part of the robot at the first position, the second position, and the intermediate position (M1-M7) as polyhedrons based on the robot data; generating a plurality of first combined approximated bodies each constituted by combining at least two robot approximated bodies of the plurality of robot approximated bodies, wherein the first combined approximated bodies are each a first cuboid that includes the at least two robot approximated bodies; generating a second combined approximated body (80, 81, 90, 91, 100) constituted by combining at least two first combined approximated bodies, wherein the second combined approximated body (80, 81, 90, 91, 100) is a first cuboid that includes the at least two first combined approximated bodies; determining whether the second combined approximated body (80, 81, 90, 91, 100) interferes with the surrounding object approximated body; and determining, if it has been determined that the second combined approximated body interferes with the surrounding object approximated body, whether the second combined approximated body interferes with a second cuboid approximated body, which is a second cuboid that includes the surrounding object, is constituted by line segments that are parallel to respective axes of a rotated coordinate system that is obtained by rotating the reference coordinate system by a given angle according to the shape of the surrounding object, and is smaller than the first cuboid. storing robot data for approximating a shape of the robot as a polyhedron for each of a plurality of movable parts (L1-L5) of the robot into the storage unit; storing data of a surrounding object approximated body that approximates the shape of the surrounding object into the storage unit, wherein the surrounding object approximated body is a first cuboid, a first cuboid being a type of cuboid constituted by line segments that are parallel to respective axes of an absolute reference coordinate system constituted by three axes that are orthogonal to each other; acquiring the first position and the second position using the acquisition unit; setting at least one intermediate position (M1-M7) on a motion path of movement from the first position to the second position; generating a plurality of robot approximated bodies that approximate the shape of at least one movable part of the robot at the first position, the second position, and the intermediate position (M1-M7) as polyhedrons based on the robot data; generating a plurality of first combined approximated bodies each constituted by combining at least two robot approximated bodies of the plurality of robot approximated bodies, wherein the first combined approximated bodies are each a first cuboid that includes the at least two robot approximated bodies; generating a second combined approximated body (80, 81, 90, 91, 100) constituted by combining at least two first combined approximated bodies, wherein the second combined approximated body (80, 81, 90, 91, 100) is a first cuboid that includes the at least two first combined approximated bodies; determining whether the second combined approximated body (80, 81, 90, 91, 100) interferes with the surrounding object approximated body; and determining, if it has been determined that the second combined approximated body interferes with the surrounding object approximated body, whether the second combined approximated body interferes with a second cuboid approximated body, which is a second cuboid that includes the surrounding object, is constituted by line segments that are parallel to respective axes of a rotated coordinate system that is obtained by rotating the reference coordinate system by a given angle according to the shape of the surrounding object, and is smaller than the first cuboid.