A fluid device (100, 110) comprising: a housing (1, 70) including an inlet and a first reservoir for liquid that has flowed in the housing (1, 70) from the inlet; a first valve mechanism including a first discharge hole for liquid provided in the first reservoir, and a float accommodated in the first reservoir and configured to open and close the first discharge hole; and a discharge valve unit comprising: a valve case configured to be detachably attached to the housing (1, 70), the valve case including a second reservoir for liquid configured to communicate with the first reservoir not through the first discharge hole but through a communication hole when the valve case is attached to the housing (1, 70); and a second valve mechanism disposed in the second reservoir, the second valve mechanism including a second discharge hole for liquid having an opening diameter larger than an opening diameter of the first discharge hole, and including a valve member accommodated in the second reservoir and configured to open and close the second discharge hole, and the second valve mechanism includes a spring configured to bias the valve member in a valve opening direction, and when a pressure of a gas or a liquid inside the second reservoir increases to a predetermined value, the valve member closes the second discharge hole under the pressure against a biasing force of the spring, characterized in that the valve case is attached to a lower portion of the first reservoir in the housing (1, 70), and an upper portion of the valve case has the communication hole configured to allow the second reservoir to communicate with the first reservoir, and the second discharge hole is open in a top-bottom direction at a bottom of the second reservoir, the valve member has a disc shape and is disposed above the second discharge hole, and the spring is disposed below the valve member and biases the valve member upward. a housing (1, 70) including an inlet and a first reservoir for liquid that has flowed in the housing (1, 70) from the inlet; a first valve mechanism including a first discharge hole for liquid provided in the first reservoir, and a float accommodated in the first reservoir and configured to open and close the first discharge hole; and a discharge valve unit comprising: a valve case configured to be detachably attached to the housing (1, 70), the valve case including a second reservoir for liquid configured to communicate with the first reservoir not through the first discharge hole but through a communication hole when the valve case is attached to the housing (1, 70); and a second valve mechanism disposed in the second reservoir, the second valve mechanism including a second discharge hole for liquid having an opening diameter larger than an opening diameter of the first discharge hole, and including a valve member accommodated in the second reservoir and configured to open and close the second discharge hole, and the second valve mechanism includes a spring configured to bias the valve member in a valve opening direction, and when a pressure of a gas or a liquid inside the second reservoir increases to a predetermined value, the valve member closes the second discharge hole under the pressure against a biasing force of the spring, characterized in that the valve case is attached to a lower portion of the first reservoir in the housing (1, 70), and an upper portion of the valve case has the communication hole configured to allow the second reservoir to communicate with the first reservoir, and the second discharge hole is open in a top-bottom direction at a bottom of the second reservoir, the valve member has a disc shape and is disposed above the second discharge hole, and the spring is disposed below the valve member and biases the valve member upward. a valve case configured to be detachably attached to the housing (1, 70), the valve case including a second reservoir for liquid configured to communicate with the first reservoir not through the first discharge hole but through a communication hole when the valve case is attached to the housing (1, 70); and a second valve mechanism disposed in the second reservoir, the second valve mechanism including a second discharge hole for liquid having an opening diameter larger than an opening diameter of the first discharge hole, and including a valve member accommodated in the second reservoir and configured to open and close the second discharge hole, and the second valve mechanism includes a spring configured to bias the valve member in a valve opening direction, and when a pressure of a gas or a liquid inside the second reservoir increases to a predetermined value, the valve member closes the second discharge hole under the pressure against a biasing force of the spring, characterized in that the valve case is attached to a lower portion of the first reservoir in the housing (1, 70), and an upper portion of the valve case has the communication hole configured to allow the second reservoir to communicate with the first reservoir, and the second discharge hole is open in a top-bottom direction at a bottom of the second reservoir, the valve member has a disc shape and is disposed above the second discharge hole, and the spring is disposed below the valve member and biases the valve member upward.