A fan (60) with a sound deadening box has in its body (3) a double inlet centrifugal fan (9) and an inlet-port sound absorber (11) formed between the fan (9) and a body air inlet (1). The fan (60) further includes a casing-inlet-port-side air passage (26) and triangular prism shaped first inlet-port-sound-absorber air passage (27). With this structure, the fan (60) has a low pressure loss, a low input, high static pressure, and a low level of airflow collision noise.