In monitoring a stratum disposal field for wastes, running tubes installed in the vicinity of a gallery or disposal holes, in a nearby rock bed, or within a gallery support or buffer members in the disposal holes have installed therein a movable monitoring device provided with various sensors, a water sampling device and the like. The monitoring device may be movable or fixed in a predetermined position, for measurement of the temperature, displacement, strain, stress and underground water in connection with the rock bed, the gallery support or the disposal space buffer members. Measurement of the clearances in the rock bed, the gallery support back or the disposal space buffer members is monitored. Also, sampling of underground water in the rock bed, the gallery support or the buffer members is effected, thus reducing the number of sensors, drilled holes, communication cables to facilitate the exchange or maintenance of the sensors, communication cables and the like. Further, the data measured by the monitoring device embedded in the buffer member or the like is transmitted by radio to a movable data collecting device in the running tube, or the data measured by the monitoring device is transmitted by radio to a management device disposed on the ground or somewhere else via a relay.