This arch-shaped beam is called a teppo beam.
Teppo means gun in Japanese, and it is so called because it is shaped like a firearm.
These beams are not molded,
but are made from the shape of a tree that has grown up with its roots bent by the weight of snow.
It is a shape unique to deep snow areas, and if the arch is utilized,
it is a reasonable structure that can withstand the weight of snow on the roof.
However, since it is a natural product, each tree is different in length,
thickness and angle, and a high level of skill is required to combine them.