We developed an arm-raising work assistance tool and evaluated its ability to mitigate the effects of the workload during grape cultivation. The tool comprises a hip belt, arm supports, and connectors linking them. This tool supports the arms when held at any height while keeping the wearer’s elbows pulled in. When performing berry thinning using the tool, the percent maximum voluntary contraction (%MVC) of the deltoid muscle was found to reduce by approximately 30%-80% without reducing the efficiency. Seven out of eight workers reported that using the tool made their work easier.