A system comprising a filter device disposed in a passage of the system, the passage being for a fluid which includes moisture in the fluid, the filter device comprising: a filter room, the filter room having a sidewall; a fluid introducing path by which fluid that flows in the passage is able to be introduced into the filter room from below the filter room; a filter placed in the filter room, the filter comprising a filter member through which the fluid introduced from the fluid introducing path into the filter room is able to permeate to remove foreign matter which may be present in the fluid; a water pooling portion (72, 78), which is provided (i) on a sidewall side at a bottom of the filter room adjacent to a periphery of the filter at a lower position than the position of the filter member, or (ii) on the filter at a lower position than the position of the filter member, or iii) on both positions (i) and (ii); and a fluid discharge path by which the fluid, having passed the filter is dischargeable, characterised in that: a gap size between the filter and the sidewall of the filter room is determined such that the water level of water collected in the water pooling portion from the moisture of the fluid during operation of the system is higher than a lower end surface of the filter member, so that the water collected in the water pooling portion (72, 78) is connected to water remaining in the filter member by surface tension and the water remaining in the filter member by surface tension can be discharged to the water pooling portion by the connection to the water in the water pooling portion. a filter room, the filter room having a sidewall; a fluid introducing path by which fluid that flows in the passage is able to be introduced into the filter room from below the filter room; a filter placed in the filter room, the filter comprising a filter member through which the fluid introduced from the fluid introducing path into the filter room is able to permeate to remove foreign matter which may be present in the fluid; a water pooling portion (72, 78), which is provided (i) on a sidewall side at a bottom of the filter room adjacent to a periphery of the filter at a lower position than the position of the filter member, or (ii) on the filter at a lower position than the position of the filter member, or iii) on both positions (i) and (ii); and (i) on a sidewall side at a bottom of the filter room adjacent to a periphery of the filter at a lower position than the position of the filter member, or (ii) on the filter at a lower position than the position of the filter member, or iii) on both positions (i) and (ii); and a fluid discharge path by which the fluid, having passed the filter is dischargeable, characterised in that: a gap size between the filter and the sidewall of the filter room is determined such that the water level of water collected in the water pooling portion from the moisture of the fluid during operation of the system is higher than a lower end surface of the filter member, so that the water collected in the water pooling portion (72, 78) is connected to water remaining in the filter member by surface tension and the water remaining in the filter member by surface tension can be discharged to the water pooling portion by the connection to the water in the water pooling portion. a gap size between the filter and the sidewall of the filter room is determined such that the water level of water collected in the water pooling portion from the moisture of the fluid during operation of the system is higher than a lower end surface of the filter member, so that the water collected in the water pooling portion (72, 78) is connected to water remaining in the filter member by surface tension and the water remaining in the filter member by surface tension can be discharged to the water pooling portion by the connection to the water in the water pooling portion.