This invention provides a sensor for the residual amount of hydrogen, which is disposed in a space where hydrogen is absorbed in and released from a hydrogen absorbing alloy as a main material.The sensor comprises a sensor body in a container form which is packed with a hydrogen absorbing alloy for a sensor and can allow the hydrogen to be moved into and moved from within the sensor body. The sensor body partially has a easy-straining part, which easily causes strain upon the release of hydrogen from the hydrogen absorbing alloy for the sensor, and a strain gage is provided for measuring the strain of the easy-straining part. Accordingly, the sensor for the residual amount of hydrogen can contribute reliable detection of the residual amount of hydrogen in the hydrogen absorbing alloy as the main material.