To satisfy various requirements such as crystallinity, corrosion resistance, wettability, melt viscosity and cracking properties by adding specified ester to flux for soldering with rosin as the main agent.

In the flux for soldering with rosin as the main agent, ester obtained by condensation reaction between a 14C-30C normal chain saturated monobasic fatty acid and polyhydric alcohol of 2-6 valances, and in which the temperature of the maximum peak in a differential heat curve lies in the range of 70 to 85C, acid value is 3 mgKOH/g and hydroxyl value is 5 mgKOH/g, is incorporated.