Abstract: An object of the present invention is to provide a novel flux, which has sufficient cleaning performance and tolerates to be used under a high flex temperature when used for so-called Pb-free solder, such as Sn—Ag or Sn—Ag—Bi based solder, and which causes no deterioration of material or no disorder in durability and; the soldering flux of the present invention is a soldering flux, in which abietic acid, the main component of rosin, is used as a main base material component, and a solid acid compound, in which a halide ion is not a constituent element, is used as the inorganic component having a function to enhance the flux activity which is added and dispersed in said rosin-based base material.