To provide an underwear including a bust-up function, capable of adjusting a capacity in a cup to the most suitable state by fitting to the right and left breast size, shape and elasticity of an individual person, and capable of regulating a bust-up degree according to a syle shape of a garment to wear.

An underwear including a bust-up adjustment function includes: a patch made of a stretchable material, and at least partially arranged in the inner surfaces of right and left cup parts; a circular member fastened to the uppermost edge of the cup part; a locking tool fastened to the top edge of the patch; a shoulder strap including a plurality of cylindrical lock holes gradually provided; and a side cloth arranged on a side adjacently to the cup part. The tip of the shoulder strap on the side of the lock hole is inserted into the circular member from an outer surface side, and fastened to the locking tool, and any of a plurality of the cylindrical lock holes is locked to the locking tool fastened to the patch. A safety through string part for inserting the patch, arranged from the chest central side to the side of the inner upper part of the cup part is also provided.