Flow path structure and cylinder block

The present invention provides a flow path structure that homogenizes the flow rate of cooling water in a water jacket and reduces pressure loss in a bypass path. The flow path structure is arranged on a component of an engine, and cooling water for cooling the engine flows in the flow path structure, and the flow path structure comprises a plurality of water jackets; the bypass passage is arranged in parallel with the plurality of water jackets; a branch passage that branches and flows the cooling water, which is pressurized by the water pump, into the most upstream water jacket among the plurality of water jackets and the most upstream portion of the bypass passage; and a plurality of connection passages connecting each of the plurality of water jackets to the bypass passage, the plurality of connection passages being connected to the bypass passage at mutually different positions from upstream to downstream of the bypass passage, and the flow passage cross-sectional areas of the plurality of connection pas