A flow rate measuring device comprising: a primary flow pipe comprising: a primary flow channel through which a fluid flows, an orifice provided in the primary flow channel and throttling a fluid flow, a first guide port, serving as a first fluid bifurcation point, provided on an upstream side of the orifice, and a first discharge port provided on a downstream side of the orifice, characterized in that the flow rate measuring device further comprises: a secondary flow channel block provided with a secondary flow channel, the secondary flow channel block being integrally provided on the primary flow pipe, one end of the secondary flow channel block communicating with the first guide port and the other end of the secondary flow channel block communicating with the first discharge port, and in that the secondary flow channel comprises: a guide flow channel in which an upstream side communicates with the first guide port, and a downstream side serves as a second fluid bifurcation point; a first secondary flow channel in which an upstream side is bifurcated from the guide flow channel at the second fluid bifurcation point and formed so as to be parallel to the primary flow channel, and a downstream side communicates with the first discharge port; a second secondary flow channel in which an upstream side is bifurcated from the guide flow channel at the second fluid bifurcation point and formed so as to cross the primary flow channel; and a detection flow channel in which an upstream side communicates with a downstream side of the second secondary flow channel, a flow rate detecting element is disposed, and a downstream side communicates with the first discharge port. a primary flow pipe comprising: a primary flow channel through which a fluid flows, an orifice provided in the primary flow channel and throttling a fluid flow, a first guide port, serving as a first fluid bifurcation point, provided on an upstream side of the orifice, and a first discharge port provided on a downstream side of the orifice, a primary flow channel through which a fluid flows, an orifice provided in the primary flow channel and throttling a fluid flow, a first guide port, serving as a first fluid bifurcation point, provided on an upstream side of the orifice, and a first discharge port provided on a downstream side of the orifice, a secondary flow channel block provided with a secondary flow channel, the secondary flow channel block being integrally provided on the primary flow pipe, one end of the secondary flow channel block communicating with the first guide port and the other end of the secondary flow channel block communicating with the first discharge port, and in that the secondary flow channel comprises: a guide flow channel in which an upstream side communicates with the first guide port, and a downstream side serves as a second fluid bifurcation point; a first secondary flow channel in which an upstream side is bifurcated from the guide flow channel at the second fluid bifurcation point and formed so as to be parallel to the primary flow channel, and a downstream side communicates with the first discharge port; a second secondary flow channel in which an upstream side is bifurcated from the guide flow channel at the second fluid bifurcation point and formed so as to cross the primary flow channel; and a detection flow channel in which an upstream side communicates with a downstream side of the second secondary flow channel, a flow rate detecting element is disposed, and a downstream side communicates with the first discharge port. a guide flow channel in which an upstream side communicates with the first guide port, and a downstream side serves as a second fluid bifurcation point; a first secondary flow channel in which an upstream side is bifurcated from the guide flow channel at the second fluid bifurcation point and formed so as to be parallel to the primary flow channel, and a downstream side communicates with the first discharge port; a second secondary flow channel in which an upstream side is bifurcated from the guide flow channel at the second fluid bifurcation point and formed so as to cross the primary flow channel; and a detection flow channel in which an upstream side communicates with a downstream side of the second secondary flow channel, a flow rate detecting element is disposed, and a downstream side communicates with the first discharge port.