Sampling the eruptive products of an active volcano is important for both understanding volcanoes and for disaster mitigation. However, when a volcano becomes active, accesses are restricted by volcanic hazard. Therefore, an unmanned sample-return system is proposed. This paper describes the system, the device, and evaluation tests in indoor simulated fields and actual volcanoes. The unmanned sample-return system consists of a multi-rotor unmanned aerial vehicle (UAV), a sampling device, and a tether to hang the device from the UAV. The sample-return scenario using this system is as follows:(0) a UAV with a camera flies into the restricted area to survey the situation, and an objective point for sampling selects from the imagery, (1) a UAV with the sampling device flies to the sampling point autonomously based on GPS, (2) at the sampling point, only the sampling device hung under the UAV lands, and it obtains a sample of the ground, (3) the UAV lifts the sampling device with the sample and returns to the takeoff point. To realize the above scenario, a roller-type sampling device was developed in this research. It weighs less than 1kg, and two parallel motor-driven rollers are attached at the bottom of the device. After the device touches down, the rollers rotate opposite each other and shave the ground. To evaluate the device, laboratory experiments were conducted in indoor simulated fields. The results of these experiments showed that the typical sampling weight was approximately 100g and the sampling depth was 15mm at most. The density of samples was almost the same as the underlying ground. The original particle size distribution of the ground was preserved in the samples in the case of well-sorted fields. The coarser particles in samples became rich by comparison in the case of poorly-sorted fields. After the laboratory experiments, field tests were conducted at actual volcanoes:Mt. Asama, Izu Oshima Island, Sakurajima Island, and Mt. Fuji. Numerous samples were obtained using the sampling device and evaluated. The results were almost universally the same as the results of the indoor experiments. However, the sampling weight decreased at both compacted ground and uneven ground sites. Long flight and full-autonomous sampling using the proposed system was successful at Mt. Fuji. In this experiment, the UAV flew for 3.2km, the device sampled pyroclasts.