An insulated electric wire includes a conductor and an insulating layer coated in periphery of the conductor. The insulating layer is made of a resin composition containing a base polymer and a flame retardant. The flame retardant is made of silane-treated aluminum hydroxide, aluminum hydroxide treated with a treatment agent other than a silane coupling agent and/or untreated aluminum hydroxide. The base polymer contains a polymer having a polar group. The resin composition contains the flame retardant, a content of which is more than 40 parts by mass and equal to or less than 80 parts by mass per 100 parts by mass of the base polymer. The resin composition contains the silane-treated aluminum hydroxide, a content of which is equal to or more than 10 parts by mass and equal to or less than 70 parts by mass per 100 parts by mass of the flame retardant.