To suppress welding defects such as blowholes caused by Zn vapor generated between galvanized steel sheets by skillfully releasing the Zn vapor without performing troublesome and difficult gap control.

In the lap melt welding method for galvanized steel sheets, an Fe based filler metal consisting mainly of Fe and containing at least one kind selected from the group consisting of viscosity lowering metals composed of Al, Si and Mn by a content(s) satisfying the inequality (a) is mixed into a molten pool. By the lowering of the viscosity of the molten pool, Zn vapor is made easy to move in the molten pool, thus Zn in the galvanizing layers is gasified, and the Zn vapor present in the molten pool can be released from the sheet faces through the molten pool, wherein (a) is 0.27Al(%)+0.044Si(%)+0.035Mn(%)≥0.32.