Diamond Thief

One of two men who plot to steal Wanyuudou's diamonds. In the original manga story, he and his friend are normal guys who just happen upon the diamonds. In the 1968 anime, Yamada is an appraiser at a jewelry store and his friend a clerk. After Junko brings her diamond to the store, Yamada pretends it is worthless and the two keep it for themselves and plot to steal the diamonds after Wanyuudou makes the aware of the location in order to lure them into his trap.

(Source: GeGeGe no Kitarou Wiki)