A filter device, comprising: a case having a bottomed tubular shape with an open upper end; a filter element having a cylindrical shape provided inside the case; a lid body provided on the case so as to cover the upper end of the case; an inflow portion and an outflow portion provided in the case, the inflow portion and the outflow portion communicating between an internal space and an external space of the case, wherein a flow path is formed in the lid body, the flow path communicating between the space inside the case and the space outside the case, and a detection unit provided in the lid body, characterized in that the lid body includes a flange portion and a cover, the flange portion having a cylindrical shape is fixed to the case, and the cover having a plate shape is provided on an upper side of the flange portion so as to cover a hollow portion of the flange portion, the cover is detachably provided to the flange portion, the detection unit is disposed at the flange portion, the flange portion has a first hole for the detection unit, the cover has a second hole for the detection unit, the second hole and the first hole are connected, the second hole and the first hole constitute the flow path, the flange portion has a side surface where an additional hole in which the detection unit is provided is formed, the additional hole has an opening covered with the detection unit by providing the detection unit in the additional hole, the first hole has one end opening to a side surface or a bottom surface of the additional hole, and the first hole and the second hole communicate between a space inside the additional hole and the space inside the case. a case having a bottomed tubular shape with an open upper end; a filter element having a cylindrical shape provided inside the case; a lid body provided on the case so as to cover the upper end of the case; an inflow portion and an outflow portion provided in the case, the inflow portion and the outflow portion communicating between an internal space and an external space of the case, wherein a flow path is formed in the lid body, the flow path communicating between the space inside the case and the space outside the case, and a detection unit provided in the lid body, characterized in that the lid body includes a flange portion and a cover, the flange portion having a cylindrical shape is fixed to the case, and the cover having a plate shape is provided on an upper side of the flange portion so as to cover a hollow portion of the flange portion, the cover is detachably provided to the flange portion, the detection unit is disposed at the flange portion, the flange portion has a first hole for the detection unit, the cover has a second hole for the detection unit, the second hole and the first hole are connected, the second hole and the first hole constitute the flow path, the flange portion has a side surface where an additional hole in which the detection unit is provided is formed, the additional hole has an opening covered with the detection unit by providing the detection unit in the additional hole, the first hole has one end opening to a side surface or a bottom surface of the additional hole, and the first hole and the second hole communicate between a space inside the additional hole and the space inside the case.