A power transmission belt (10) includes: a belt body (11) including a part (14) which is in contact with a flat pulley and which is made of a rubber composition containing an ethylene-α-olefin elastomer with an ethylene content of less than or equal to 60% by mass as raw rubber. The rubber composition forming the contact part (14) with the flat pulley has a storage modulus of 20-60 MPa at 25° C. and a storage modulus of 12 MPa or more at 100° C., short fibers are not blended into the rubber composition, and the grain direction of the rubber composition corresponds to a belt lengthwise direction.