A machine tool system, comprising a spindle configured such that a tool is mounted on a distal end part thereof, a tool magazine which holds a plurality of tools, a tool exchange arm which exchanges tools between the tool magazine and the rotating spindle, and a table to which a workpiece is attached, wherein the workpiece is machined by moving the spindle and the table relative to each other in accordance with a machining program, the machine tool system comprising: an imaging device which generates an image of the tool mounted on a tool holder along with the tool holder, wherein the tool holder has a gauge line, and wherein the image of the tool generated by the imaging device includes a holder part, which is a portion which holds the tool, and a tool part, which is a portion of the tool protruding from the tool holder; a storage unit configured to store threshold values related to a tool length (L' T), a diameter of the tool part (D' T) and a diameter of the holder part (D' H); an interference checking device which simulates machining, prior to machining, using the machining program and shape data of the workpiece, the tool, and a machine tool to confirm the presence or absence of interference between at least the tool and the workpiece, and a controller which acquires the shape data of the tool mounted on the tool holder from the interference checking device, generates a two-dimensional tool model from the acquired shape data of the tool in which the tool mounted on the tool holder and the tool holder are projected onto a plane, compares a tool length (L' T), which is an axial direction length from the gauge line to the distal end of the tool, a diameter of the tool part (D' T) and a diameter of the holder part (D' H) of the two-dimensional tool model and the image of the tool imaged by the imaging device, and determines that the tool is invalid when a deviation between the tool length (L' T), the diameter of the tool part (D' T) or the diameter of the holder part(D' H) of the two-dimensional tool model and the image data is equal to or greater than the corresponding threshold value stored in the storage unit. an imaging device which generates an image of the tool mounted on a tool holder along with the tool holder, wherein the tool holder has a gauge line, and wherein the image of the tool generated by the imaging device includes a holder part, which is a portion which holds the tool, and a tool part, which is a portion of the tool protruding from the tool holder; a storage unit configured to store threshold values related to a tool length (L' T), a diameter of the tool part (D' T) and a diameter of the holder part (D' H); an interference checking device which simulates machining, prior to machining, using the machining program and shape data of the workpiece, the tool, and a machine tool to confirm the presence or absence of interference between at least the tool and the workpiece, and a controller which acquires the shape data of the tool mounted on the tool holder from the interference checking device, generates a two-dimensional tool model from the acquired shape data of the tool in which the tool mounted on the tool holder and the tool holder are projected onto a plane, compares a tool length (L' T), which is an axial direction length from the gauge line to the distal end of the tool, a diameter of the tool part (D' T) and a diameter of the holder part (D' H) of the two-dimensional tool model and the image of the tool imaged by the imaging device, and determines that the tool is invalid when a deviation between the tool length (L' T), the diameter of the tool part (D' T) or the diameter of the holder part(D' H) of the two-dimensional tool model and the image data is equal to or greater than the corresponding threshold value stored in the storage unit.