A flux in which solder wettability can be maintained and with which it is possible to suppress the amount of residue after soldering and realize low residue. This flux includes 65-99 wt % of a solvent, and also includes 1-13 wt % of at least one acid selected form a dimer acid that is a reaction product of oleic acid and linoleic acid; a trimer acid that is a reaction product of oleic acid and linoleic acid; a hydrogenated dimer acid obtained by hydrogenating dimer acid that is a reaction product of oleic acid and linoleic acid; and a hydrogenated trimer acid obtained by hydrogenating a trimer acid that is a reaction product of oleic acid and linoleic acid.