To provide a lead wire for narrow space insertion that is easily inserted into an elongated small-diameter pipe or small-diameter tube such as an ultrasonic probe or an electrode catheter. The above-described problem is solved by a lead wire for narrow space insertion including a copper alloy wire having a conductor diameter within a range of 0.015 to 0.18 mm, and an insulating layer provided to an outer periphery of the copper alloy wire. A friction coefficient of an outermost surface layer of the insulating layer is within a range of 0.05 to 0.3, a tensile strength of the lead wire is within a range of 700 to 1,500 MPa, and a conductivity of the copper alloy wire is within a range of 60 to 90% IACS.