A ray filter for use in a dual-energy X ray inspection system configured to emit high-energy X-rays and low-energy X-rays, wherein the ray filter is switchable between a first state where the ray filter is configured to allow high-energy X-rays and low-energy X-rays emitted from an X-ray source to pass therethrough and a second state where the ray filter is configured to only allow the high-energy X-rays to pass therethrough, wherein the ray filter comprises a ray filter body having a first slit opening through which the X-rays are emitted and which is an elongate slit opening, and a shielding member which is an elongate cylindrical rod, wherein the shielding member is provided in the ray filter body in a direction perpendicular to a direction in which the rays are emitted, and wherein the shielding member is arranged so that it can be rotated, wherein the shielding member comprises a second slit opening that runs through said shielding member to form a slit-like through hole, and the shielding member is arranged to switch the ray filter between the first state and the second state through the rotation, wherein, in the first state, the second slit opening is aligned with the first slit opening so as to form a passage for allowing the rays to pass through the first slit opening and the second slit opening, and wherein, in the second state, the second slit opening is shifted from the first slit opening so that the first slit opening is blocked by a solid portion of the shielding member, wherein in the second state the shielding member has a planar exterior surface portion through which the high-energy X-rays are transmitted and the face of the shielding member from which the X-rays are emitted is also planar. wherein the ray filter is switchable between a first state where the ray filter is configured to allow high-energy X-rays and low-energy X-rays emitted from an X-ray source to pass therethrough and a second state where the ray filter is configured to only allow the high-energy X-rays to pass therethrough, wherein the ray filter comprises a ray filter body having a first slit opening through which the X-rays are emitted and which is an elongate slit opening, and a shielding member which is an elongate cylindrical rod, wherein the shielding member is provided in the ray filter body in a direction perpendicular to a direction in which the rays are emitted, and wherein the shielding member is arranged so that it can be rotated, wherein the shielding member comprises a second slit opening that runs through said shielding member to form a slit-like through hole, and the shielding member is arranged to switch the ray filter between the first state and the second state through the rotation, wherein, in the first state, the second slit opening is aligned with the first slit opening so as to form a passage for allowing the rays to pass through the first slit opening and the second slit opening, and wherein, in the second state, the second slit opening is shifted from the first slit opening so that the first slit opening is blocked by a solid portion of the shielding member, wherein in the second state the shielding member has a planar exterior surface portion through which the high-energy X-rays are transmitted and the face of the shielding member from which the X-rays are emitted is also planar.