An insertion frame structure comprising: - a pair of groove-shaped primary members whose cross-sectional shapes are, at least partially, angular U shapes, and which are placed being separated by a predetermined distance and facing to each other symmetrically with respect to a center line passing the midpoint of the predetermined distance; and - a plurality of auxiliary members whose cross-sectional shapes are, at least partially, L shapes, and which are placed between the primary members, wherein - the primary members and the auxiliary members are joined with each other at their latch portions (11, 21), - the primary members are placed with a bottom portion of the groove shape facing downward, - at a latch portion of each of the primary members, the height of one of walls which is closer to the center line side is lower than the height of the other wall on the outer side, - at the latch portion of each of the primary members, latch holes (11a 11b, 11c) with a clearance shape are formed in the one wall, the bottom portion, and the other wall, - the latch portion of each of the auxiliary member has: a first convex portion to be inserted into the latch hole formed in the other wall; a second convex portion to be inserted into the latch hole formed in the bottom portion; and a third convex portion to be inserted into the latch hole formed in the one wall, and - each of the latch holes (11a, 11b, 11c) has a clearance with a larger dimension than a plate thickness (t) of the auxiliary member, and has, continuously from the clearance, a clearance with a dimension equal to the plate thickness (t) of the auxiliary member or smaller than the plate thickness (t) of the auxiliary member. - a pair of groove-shaped primary members whose cross-sectional shapes are, at least partially, angular U shapes, and which are placed being separated by a predetermined distance and facing to each other symmetrically with respect to a center line passing the midpoint of the predetermined distance; and - a plurality of auxiliary members whose cross-sectional shapes are, at least partially, L shapes, and which are placed between the primary members, wherein - the primary members and the auxiliary members are joined with each other at their latch portions (11, 21), - the primary members are placed with a bottom portion of the groove shape facing downward, - at a latch portion of each of the primary members, the height of one of walls which is closer to the center line side is lower than the height of the other wall on the outer side, - at the latch portion of each of the primary members, latch holes (11a 11b, 11c) with a clearance shape are formed in the one wall, the bottom portion, and the other wall, - the latch portion of each of the auxiliary member has: a first convex portion to be inserted into the latch hole formed in the other wall; a second convex portion to be inserted into the latch hole formed in the bottom portion; and a third convex portion to be inserted into the latch hole formed in the one wall, and - each of the latch holes (11a, 11b, 11c) has a clearance with a larger dimension than a plate thickness (t) of the auxiliary member, and has, continuously from the clearance, a clearance with a dimension equal to the plate thickness (t) of the auxiliary member or smaller than the plate thickness (t) of the auxiliary member.