Provided are a low-noise, high-performance multiblade centrifugal fan that suppresses interference between rotational flows generated within extension sections that are extended in a rotation-axis direction at upper and lower end surfaces of a scroll casing, and an air conditioner equipped with the same. In a multiblade centrifugal fan having an impeller disposed in a rotatable manner about a rotation shaft within a scroll casing having a flow path whose cross section gradually increases in a rotational direction, at least one of upper and lower end surfaces of the scroll casing serves as an inclined end surface that is extended in the extending direction of the rotation shaft such that an extended height thereof gradually increases in the rotational direction from a scroll start position, and a stepped section extending in the rotational direction is provided between the inclined end surface and an inner-peripheral side surface of an extension section.