A static fluid mixer which can perform processing such as generation of ultrafine uniform bubbles and has small pressure loss. A static fluid mixer has mixing units having outflow openings for allowing fluid having passed through mixing flow paths to flow through the outflow openings. The mixing units are arranged in a tubular casing body at intervals in the axis direction of the casing body. Adjacent mixing units and the casing body form a flow path forming space. Each mixing unit has an annular outflow path communicating with the end of each mixing flow path. The annular outflow path is open in a ring-like form having a substantially constant width along the entire circumference. The opening at the end of the annular outflow path functions as an outflow opening connecting to the flow path forming space. In the outflow path forming space is formed a collection flow path into which liquid having passed through the mixing flow path collects after flowing from the entire circumference of the outflow opening which is open in the ring-like form and moving toward the axis of the casing body.