A valve system has a main body including a valve element that controls flow of fluid between a plurality of ports and an operation unit capable of being detachably attached to the main body. The main body includes: a driving element that is operated from the outside by a magnetic force and directly or indirectly drives the valve element; and a first housing that houses the valve element and the driving element and is watertight in a state where pipes are connected to the plurality of ports. The operation unit includes: an operation element that generates a magnetic field that operates the driving element; and a second housing that houses the operation element, when attached to the first housing, the operation element and the driving element being in a facing state via part of a wall of the first housing and part of a wall of the second housing.