A silane-crosslinked polyolefin insulated wire includes a conductor, and an insulating cover layer extruded on an outer periphery of the conductor. The insulating cover layer includes a silane-crosslinked polyolefin to be cross-linked by reacting water with a polyolefin having an alkoxysilyl group as a side chain. The insulating cover layer further includes a guanidine derivative having a boiling point of not less than 170° C. and a melting point of less than 190° C. in an environment at 760 mmHg as a crosslinking promoter to promote crosslinking of the polyolefin in an amount of not less than 0.05 parts by mass and not more than 0.5 parts by mass per 100 parts by mass of the polyolefin.