PURPOSE: To prevent an oil hydraulic motor from its action at neutral time of a static oil pressure transmission by a simple structure and inexpensively.

CONSTITUTION: An oil relief path 36, formed of a groove for connecting blow and delivery ports 31, 32 of a valve plate, is formed in the valve plate 30 of an oil hydraulic pump 1 of a static oil pressure transmission formed by connecting an oil hydraulic pump 1 to an oil hydraulic motor 4 in a closed circuit state, to relieve oil, delivered a little from the oil hydraulic pump at neutral time, to a blow side from a delivery side of the blow and delivery ports 31, 32 through an oil relief path 36, so that oil is prevented from being fed to the oil hydraulic motor.