A carbon-fiber-precursor acrylic fiber bundle which can smoothly pass through a flame-resistance impartation step and a carbonization step. The carbon-fiber-precursor acrylic fiber bundle has a high-density part as a portion thereof, wherein the high-density part satisfies the following requirements (A) and (B). Requirement A: The high-density part has a maximum fiber density ρmax of 1.33 g/cm3 or higher. Requirement B: The portion extending between an intermediate-density point and a maximum-density-region arrival point has an increase in fiber density of 1.3×10−2 g/cm3 or less per 10 mm of the fiber bundle length.