PURPOSE: To provide a polyester conjugated bulky pre-treated yarn having excellent adhesiveness to coating resins and suitable for applications such as belts requiring good dynamic adhesive durability.

CONSTITUTION: A polyester conjugated bulky pre-treated yarn having the following characteristics, (A) 0.01-0.5% of an aliphatic polyfunctional epoxy compound and (B) 0.1-5% of a polyallylamine being stuck to the surface of the conjugated yarn. (a) The core fibers are arranged substantially linearly. (b) The sheath fibers are partially interlaced with the core fibers, but most of the single filaments composing the sheath fibers exhibit curved states on the surface of the conjugated yarn. (c) The proportion of the sheath fibers is 3-20%.