A strainer provided in a refrigerant piping of an air conditioning device through which refrigerant flows includes a cylindrical shell disposed in the refrigerant piping, a cage type filter which includes an opening at one end and a bottom at the other end facing with each other relative to the flowing direction of the refrigerant and a meshed circumferential portion for allowing the refrigerant to pass through, but preventing sludge to pass through an annular passage provided between an outer circumferential portion of the filter and an inner circumferential portion of the cylindrical shell for the refrigerant to flow through and a leading pipe inserted into the refrigerant piping for letting the refrigerant and sludge and having an opening disposed in the cylindrical shell adjacent and opposing to the bottom of the filter and an inner circumferential wall along which sludge flows.