To provide an acrylic fiber bundle as a carbon fiber precursor capable of producing a carbon fiber bundle having excellent operational stability and excellent mechanical characteristics while excellently maintaining a fusion-proof property between single filaments even when the carbon fiber bundle having a large number of single filaments is produced.

An acrylic fiber bundle as a carbon fiber precursor has single filament fineness of 1.0 to 3.0 dTex, comprises single filaments of 24000 or more, and satisfies the following requirements [a] to [e]: [a] An oil component having 0.03 second or less of a difference in vibrational period of a pendulum between at 30°C and at 180°C, measured by a free vibration decay method of a rigid pendulum, is adhered to the fiber in an amount of 0.05 to 3 mass% based on dry fiber weight; [b] Si content is 0.1 to 0.9 mass% based on dry fiber weight; [c] Electrical resistivity is 1.0×10¹² Ω or less; [d] A ratio of a major axis to a minor axis of the cross section of a single filament (the major axis/the minor axis) is 1.1 to 1.5; and [e] The maximum height (Ry) of the surface of the single filament is 0.3 to 0.6 μm.