A tumor reductive procedure under ultrasound observation includes observing a tissue from an inside or an outside of a body with an ultrasound observation device, dissolving, breaking up, resecting, or vaporizing a tumor inner portion under ultrasound observation by the ultrasound observation device, introducing a solvent for suspension into the tumor inner portion from a distal end of a needle tube arranged in the tumor inner portion, mixing the solvent for suspension with a tumor tissue of the dissolved, broken-up, resected, or vaporized tumor inner portion, and changing the tumor inner portion to a fluid, and collecting the tumor tissue, which is mixed with the solvent for suspension and softened, from the tumor inner portion using the needle tube or another duct after changing the tumor to the fluid under the ultrasound observation.
