To provide sole materials for shoes which can be manufactured by a simple and accordingly convenient form of manufacturing technique on one side and arbitrarily vary density in the lateral direction across whole zones of the sole members on the other side.

A sole member preform 20 is manufactured from a plastic material with thickness variation in the lateral direction according to desired density distribution. The sole material preform 20 is press-formed in a forming tool to form the finished sole member from the sole element preform 20. Desired density distribution is adjusted so as to gradually increase density from the outside 5 of the sole member toward the inside 10.