A permeameter for in-situ measurement of saturated hydraulic conductivity is presented. The permeameter includes a chamber fixedly installed into streambed sediment such that the inside of the chamber is filled with a medium, sediment at water-sediment interface. First and second hydraulic head-measuring lines are respectively connected to upper and lower portions of an outer circumferential surface of the chamber, these are designed for measuring a hydraulic head difference of the inside of the chamber. A flexible tube is interconnected the chamber with the storage pipe. A storage pipe is designed to regulate a hydraulic head difference from the chamber and to measure a quantity and a flow rate of water introduced from the chamber under the streambed.