Method for producing insulated electric wire

A method for producing an insulated electric wire comprises a first step of processing a copper alloy containing a tin and inevitable impurities into a fine wire having a diameter of 0.21 mm±0.008 mm, the tin being 0.30 wt % or more and 0.39 wt % or less, a second step of annealing the fine wire obtained in the first step so as to refine the fine wire to have an extension coefficient of 10% or more and 25% or less and a tensile strength of 300 MPa or more and 400 MPa or less, and a third step of twisting the seven fine wires having undergone the second step with a twist pitch of 15 mm±6 mm.