In a float device including a floating body, the floating body includes: a main body part having a first surface, a second surface opposite the first surface, and a first side surface connecting the first surface and the second surface; and at least a first joining part and a second joining part located on the first side surface to locate on both sides in a first direction parallel to a ridge line defined by the first surface and the first side surface. The first joining part and the second joining part each include a first portion located on the first side surface and a second portion connected to the first portion to face the first side surface. The second portion includes an end portion farthest from the first portion. An end portion of the first joining part and an end portion of the second joining part face each other. A minimum distance D1 between the end portion of the first joining part and the end portion of the second joining part is greater than twice a width D2 of the second portion of the first joining part in the first direction, and is smaller than a minimum distance D3 between the first portion of the first joining part and the first portion of the second joining part.