A suturing and ligating method includes a needle piercing step of inserting a needle of a suture-needle assembly through a tissue in a body cavity, a needle gripping step of gripping the needle with a first gripper, a winding step of winding a suture strand of the suture-needle assembly in at least one turn around a first distal-end working unit by rolling the first distal-end working unit in at least one revolution, a transferring step of transferring the suture-needle assembly from the first gripper to a second gripper, a suture strand gripping step of gripping a portion of the suture strand that has not passed through the tissue, with the first gripper, a pulling step of pulling the first distal-end working unit out of a loop of the suture strand, and a tightening step of forming a knot of the suture strand.