A differential pressure type flowmeter comprising: a main flow channel configured to allow fluid to flow; an orifice provided in the main flow channel; an upstream pressure sensor configured to detect pressure of fluid on an upstream side of the orifice; a downstream pressure sensor configured to detect pressure of fluid on a downstream side of the orifice; a first flow channel communicating with the main flow channel, and configured to guide the fluid on the upstream side of the orifice to the upstream pressure sensor; and a second flow channel communicating with the main flow channel, and configured to guide the fluid on the downstream side of the orifice to the downstream pressure sensor, wherein the upstream pressure sensor includes a first sensor body that detects pressure of fluid which flows from the main flow channel into a first fluid chamber through the first flow channel, the downstream pressure sensor includes a second sensor body that detects pressure of fluid which flows from the main flow channel into a second fluid chamber through the second flow channel, a first flow channel length of the first flow channel coincide with a second flow channel length of the second flow channel, the first flow channel length being a length from the main flow channel to an inlet of the first fluid chamber, the second flow channel length being a length from the main flow channel to an inlet of the second fluid chamber, a first flow channel diameter of the first flow channel coincide with a second flow channel diameter of the second flow channel, characterised in that: a ratio of the first flow channel length to the first flow channel diameter and a ratio of the second flow channel length to the second flow channel diameter are not less than 20 times and not more than 30 times, respectively. a main flow channel configured to allow fluid to flow; an orifice provided in the main flow channel; an upstream pressure sensor configured to detect pressure of fluid on an upstream side of the orifice; a downstream pressure sensor configured to detect pressure of fluid on a downstream side of the orifice; a first flow channel communicating with the main flow channel, and configured to guide the fluid on the upstream side of the orifice to the upstream pressure sensor; and a second flow channel communicating with the main flow channel, and configured to guide the fluid on the downstream side of the orifice to the downstream pressure sensor, wherein the upstream pressure sensor includes a first sensor body that detects pressure of fluid which flows from the main flow channel into a first fluid chamber through the first flow channel, the downstream pressure sensor includes a second sensor body that detects pressure of fluid which flows from the main flow channel into a second fluid chamber through the second flow channel, a first flow channel length of the first flow channel coincide with a second flow channel length of the second flow channel, the first flow channel length being a length from the main flow channel to an inlet of the first fluid chamber, the second flow channel length being a length from the main flow channel to an inlet of the second fluid chamber, a first flow channel diameter of the first flow channel coincide with a second flow channel diameter of the second flow channel, characterised in that: a ratio of the first flow channel length to the first flow channel diameter and a ratio of the second flow channel length to the second flow channel diameter are not less than 20 times and not more than 30 times, respectively.