A fire detector comprising: a light-emitting portion that repeats stopping of light emission and outputting light emission a plurality of times in every predetermined light emission period during a predetermined smoke detection operation time in every predetermined first period; a light-receiving portion that receives the light emitted from the light-emitting portion and outputs a light reception signal during the smoke detection operation time; a light reception signal detecting portion that detects as a zero-point light reception signal the light reception signal that the light-receiving portion outputs at each light emission stop timing of the smoke detection operation time, and detects as a smoke light reception signal the light reception signal that the light-receiving portion outputs at each light emission timing; and a smoke detecting portion that detects a smoke detection signal based on the zero-point light reception signals of a plurality of times and the smoke light reception signals of a plurality of times detected by the light reception signal detecting portion, characterized in that the fire detector further comprises: a noise assessing-processing portion that assesses the presence of mixing-in of noise to the light reception signal based on the zero-point light reception signals of a plurality of times and the smoke light reception signals of a plurality of times, and carries out noise removal processing in a case of having assessed that the noise is mixed in, wherein the noise assessing-processing portion includes a third noise assessment mode that assesses the noise as being mixed in when the difference between the maximum value and the minimum value of the smoke light reception signals of a plurality of times is greater than or equal to a predetermined threshold value; and a fifth noise assessment mode that assesses the noise as being mixed in when any of the zero-point light reception signals of a plurality of times exceeds the smoke light reception signals detected next, and the noise assessing-processing portion carries out the noise removal processing in a case of having assessed that the noise is mixed in based on one or both of the third noise assessment mode and the fifth noise assessment mode. a light-emitting portion that repeats stopping of light emission and outputting light emission a plurality of times in every predetermined light emission period during a predetermined smoke detection operation time in every predetermined first period; a light-receiving portion that receives the light emitted from the light-emitting portion and outputs a light reception signal during the smoke detection operation time; a light reception signal detecting portion that detects as a zero-point light reception signal the light reception signal that the light-receiving portion outputs at each light emission stop timing of the smoke detection operation time, and detects as a smoke light reception signal the light reception signal that the light-receiving portion outputs at each light emission timing; and a smoke detecting portion that detects a smoke detection signal based on the zero-point light reception signals of a plurality of times and the smoke light reception signals of a plurality of times detected by the light reception signal detecting portion, characterized in that the fire detector further comprises: a noise assessing-processing portion that assesses the presence of mixing-in of noise to the light reception signal based on the zero-point light reception signals of a plurality of times and the smoke light reception signals of a plurality of times, and carries out noise removal processing in a case of having assessed that the noise is mixed in, wherein the noise assessing-processing portion includes a third noise assessment mode that assesses the noise as being mixed in when the difference between the maximum value and the minimum value of the smoke light reception signals of a plurality of times is greater than or equal to a predetermined threshold value; and a fifth noise assessment mode that assesses the noise as being mixed in when any of the zero-point light reception signals of a plurality of times exceeds the smoke light reception signals detected next, a noise assessing-processing portion that assesses the presence of mixing-in of noise to the light reception signal based on the zero-point light reception signals of a plurality of times and the smoke light reception signals of a plurality of times, and carries out noise removal processing in a case of having assessed that the noise is mixed in, wherein the noise assessing-processing portion includes a third noise assessment mode that assesses the noise as being mixed in when the difference between the maximum value and the minimum value of the smoke light reception signals of a plurality of times is greater than or equal to a predetermined threshold value; and a fifth noise assessment mode that assesses the noise as being mixed in when any of the zero-point light reception signals of a plurality of times exceeds the smoke light reception signals detected next, and the noise assessing-processing portion carries out the noise removal processing in a case of having assessed that the noise is mixed in based on one or both of the third noise assessment mode and the fifth noise assessment mode.