Flow rate calculation device and flow rate calculation method

A flow rate calculation device that calculates a flow rate of a fluid flowing through a main flow path, the flow rate calculation device comprising:

• a specific flow path and a bypass flow path
• which are provided to branch from the main flow path and
• to which the fluid is diverted;
• a first fluid resistance element that is provided in the specific flow path;
• a second fluid resistance element that is provided in the bypass flow path;
• a container that is arranged on a downstream side of the first fluid resistance element in the specific flow path;
• a pressure sensor that detects a pressure in the container;
• and
• a flow rate calculation unit that
• calculates a flow rate of a first branch fluid diverted to the specific flow path based on a change in the pressure in the container, and
• calculates the flow rate of the fluid flowing through the main flow path based on the calculated flow rate of the first branch fluid and a diversion ratio determined according to the first fluid resistance element and the second fluid resistance element.