A random mat includes a chopped fiber bundle [A] obtained by obliquely cutting a partially separated fiber bundle [B] prepared by alternately forming separation-processed sections, each of which is separated into a plurality of bundles, and not-separation-processed sections, along the lengthwise direction of a fiber bundle, wherein the total cross-sectional area of reinforcing fibers exhibits a specific change amount between both tips of the chopped fiber bundle [A]; a production method produces the random mat; and a fiber-reinforced resin molding material uses the random mat.