A counter-rotating axial flow fan with improved characteristics and reduced noise compared to the related art can be provided. Defining the number of front blades as N, the number of stationary blades as M, and the number of rear blades as P, and defining the maximum axial chord length of the front blades as Lf, the maximum axial chord length of the rear blades as Lr, the outside diameter of the front blades as Rf, and the outside diameter of the rear blades as Rr, the counter-rotating axial flow fan satisfies the following two relationships: N≧P>M; and Lf/(Rf×π/N)≧1.25 and/or Lr/(Rr×π/P)≧0.83.