A vehicle body frame structure comprising: a side frame that is arranged on one of a front side and a rear side of a cabin along a vehicle body longitudinal direction; a sub-frame that is arranged below the side frame and supports a suspension component; a cabin side support member that is arranged outside and below one of a front section and a rear section of the cabin, and that supports an end portion of the sub-frame which is at a side adjacent to the cabin; an under-floor frame that is arranged below a stepped portion of a floor adjacent to a floor tunnel portion of the cabin, along the vehicle body longitudinal direction; and a link stay that is arranged across and connects together the end portion of the side adjacent to the cabin in the sub-frame and the under-floor frame, wherein the sub-frame includes: a separate side fastening portion which is an end portion on a side separating from the cabin and is fastened to a member on an extension end side of the side frame; an adjacent side fastening portion which is the end portion on the side adjacent to the cabin and is fastened and fixed to the cabin side support member from a lower side; and a central bending point which is configured to be bent down at a substantially central portion in between of the separate side fastening portion and the adjacent side fastening portion in the longitudinal direction, wherein in the link stay, a first end portion side of the link stay is fastened to a lower surface of the cabin side support member together with the adjacent side fastening portion so as to be extractable, and a second end portion side of the link stay is fastened to the under-floor frame by a support bolt extending in a vehicle width direction and a nut screwed to the support bolt, wherein the nut for fastening the second end portion side of the link stay is held by a lateral wall on a side separating from the floor tunnel portion of the link stay, and wherein the support bolt is fitted into the nut from a lower side of the floor tunnel portion. a side frame that is arranged on one of a front side and a rear side of a cabin along a vehicle body longitudinal direction; a sub-frame that is arranged below the side frame and supports a suspension component; a cabin side support member that is arranged outside and below one of a front section and a rear section of the cabin, and that supports an end portion of the sub-frame which is at a side adjacent to the cabin; an under-floor frame that is arranged below a stepped portion of a floor adjacent to a floor tunnel portion of the cabin, along the vehicle body longitudinal direction; and a link stay that is arranged across and connects together the end portion of the side adjacent to the cabin in the sub-frame and the under-floor frame, wherein the sub-frame includes: a separate side fastening portion which is an end portion on a side separating from the cabin and is fastened to a member on an extension end side of the side frame; an adjacent side fastening portion which is the end portion on the side adjacent to the cabin and is fastened and fixed to the cabin side support member from a lower side; and a central bending point which is configured to be bent down at a substantially central portion in between of the separate side fastening portion and the adjacent side fastening portion in the longitudinal direction, wherein in the link stay, a first end portion side of the link stay is fastened to a lower surface of the cabin side support member together with the adjacent side fastening portion so as to be extractable, and a second end portion side of the link stay is fastened to the under-floor frame by a support bolt extending in a vehicle width direction and a nut screwed to the support bolt, wherein the nut for fastening the second end portion side of the link stay is held by a lateral wall on a side separating from the floor tunnel portion of the link stay, and wherein the support bolt is fitted into the nut from a lower side of the floor tunnel portion. a separate side fastening portion which is an end portion on a side separating from the cabin and is fastened to a member on an extension end side of the side frame; an adjacent side fastening portion which is the end portion on the side adjacent to the cabin and is fastened and fixed to the cabin side support member from a lower side; and a central bending point which is configured to be bent down at a substantially central portion in between of the separate side fastening portion and the adjacent side fastening portion in the longitudinal direction, wherein in the link stay, a first end portion side of the link stay is fastened to a lower surface of the cabin side support member together with the adjacent side fastening portion so as to be extractable, and a second end portion side of the link stay is fastened to the under-floor frame by a support bolt extending in a vehicle width direction and a nut screwed to the support bolt, wherein the nut for fastening the second end portion side of the link stay is held by a lateral wall on a side separating from the floor tunnel portion of the link stay, and wherein the support bolt is fitted into the nut from a lower side of the floor tunnel portion.