A fan with a sound muffling box includes a box having a box inlet port and a box outlet port located on opposite sides from each other; and a double suction centrifugal fan encased in the box. The centrifugal fan includes a motor, a discharge port, an impeller, a scroll, and a casing side plate. The casing side plate has a motor-side inlet port, and an opposite-motor-side inlet port opposite to the motor-side inlet port with respect to the impeller. The discharge port is inclined with respect to the box outlet port. The fan with the sound muffling box further includes a sound insulating board disposed on the box inlet port in such a manner as to hide the opposite-motor-side inlet port and also to divide the box inlet port into plural regions when the inside of the box is viewed from the box inlet port.