This gas measuring device (1) is provided with: a plurality of measuring channels (22a, 22b, 22c) provided in parallel between an inlet into which a fluid flows, and an outlet from which said fluid flows; flow rate measuring units (61a, 61b, 61c) that are provided to each of the measuring channels (22a, 22b, 22c), and determine the amount of fluid that flows through the measuring channels (22a, 22b, 22c); memory units (62a, 62b, 62c) which, for each measuring path (22a, 22b, 22c), retain coefficient data comprising values representing the relationship between the amount of fluid that flows through each measuring channel (22a, 22b, 22c) and the total flow of fluid that flows through the outlet from the inlet; and total flow estimating units (60a, 60b, 60c) that estimate the total flow of fluid on the basis of the amounts determined by the flow rate measuring units (61a, 61b, 61c) and the coefficient data retained in the memory units (62a, 62b, 62c). The time required for adjustment work in a step for manufacturing fluid measuring devices assembled by connecting a plurality of measuring channels in parallel can thus be reduced.