The frame body is formed by a plurality of pipe-shaped members including a first column portion, a beam portion, the front end portion of which is connected to the upper end portion of the first column portion, and a middle column member that is disposed rearward from the first column portion. The upper guide portion is provided along a beam portion in a position ranging from a first position to a second position. Here, the first position is located frontward from the middle column member and rearward from the first column portion, and the second position is located rearward from the middle column member.