Abstract: A pressure converter insusceptible to the error of hydraulic pressure introducing position or the interference of installation depth of water and producing a signal corresponding to the effective soil pressure accurately while realizing cost reduction. Since filters are provided in an air gap defined by two rigid plates receiving the soil pressure, a hydraulic pressure is applied but sand pressure is not applied. A load gauge insensitive to the hydraulic pressure detects only the effective soil pressure. Since a signal cable can be passed through the air gap, a plurality of pressure converters can be coupled efficiently and since the signal cable can be inserted internally, a pressure distributed in the depth direction can also be measured accurately.