The present invention provides a Sn--Zn based lead-free solder which can prevent peeling of solder from soldered portions even after the passage of long periods after soldering of portions to be soldered made of Cu. A Sn--Zn based lead-free solder according to the present invention comprises 5-10 mass percent of Zn, a total of 0.005-1.0 mass percent of at least one substance selected from the group consisting of Au, Pt, Pd, Fe, and Sb, optionally a total of at most 15 mass percent of at least one substance selected from the group consisting of Bi and In, and a remainder of Sn. This Sn--Zn based lead-free solder can be made into a solder paste using a rosin flux containing a halide such as an amine hydrochloride as an activator.