A centrifugal fan comprising: a fan configured to be driven to rotate; and a scroll casing housing the fan ; the scroll casing including a peripheral wall having a volute shape having an inner end of a spiral thereof at a boundary with a tongue portion of the scroll casing , the tongue portion being configured to guide airflow generated by the fan , the peripheral wall including, when a portion at the peripheral wall at which a distance between the peripheral wall and a rotation shaft (RS) of the fan is minimum is defined as a closest portion , a narrowed portion at which the distance between the peripheral wall and the rotation shaft (RS) is reduced from the inner end toward the closest portion in a rotation direction of the fan , and an expanded portion (4c1) that is formed between the narrowed portion and the closest portion and at which the distance between the peripheral wall and the rotation shaft (RS) is increased or the distance between the peripheral wall and the rotation shaft (RS) is constant. a fan configured to be driven to rotate; and a scroll casing housing the fan ; the scroll casing including a peripheral wall having a volute shape having an inner end of a spiral thereof at a boundary with a tongue portion of the scroll casing , the tongue portion being configured to guide airflow generated by the fan , the peripheral wall including, when a portion at the peripheral wall at which a distance between the peripheral wall and a rotation shaft (RS) of the fan is minimum is defined as a closest portion , a narrowed portion at which the distance between the peripheral wall and the rotation shaft (RS) is reduced from the inner end toward the closest portion in a rotation direction of the fan , and an expanded portion (4c1) that is formed between the narrowed portion and the closest portion and at which the distance between the peripheral wall and the rotation shaft (RS) is increased or the distance between the peripheral wall and the rotation shaft (RS) is constant. a peripheral wall having a volute shape having an inner end of a spiral thereof at a boundary with a tongue portion of the scroll casing , the tongue portion being configured to guide airflow generated by the fan , the peripheral wall including, when a portion at the peripheral wall at which a distance between the peripheral wall and a rotation shaft (RS) of the fan is minimum is defined as a closest portion , a narrowed portion at which the distance between the peripheral wall and the rotation shaft (RS) is reduced from the inner end toward the closest portion in a rotation direction of the fan , and an expanded portion (4c1) that is formed between the narrowed portion and the closest portion and at which the distance between the peripheral wall and the rotation shaft (RS) is increased or the distance between the peripheral wall and the rotation shaft (RS) is constant. a narrowed portion at which the distance between the peripheral wall and the rotation shaft (RS) is reduced from the inner end toward the closest portion in a rotation direction of the fan , and an expanded portion (4c1) that is formed between the narrowed portion and the closest portion and at which the distance between the peripheral wall and the rotation shaft (RS) is increased or the distance between the peripheral wall and the rotation shaft (RS) is constant. <EOS>