Auditory selective attention plays a key role in the cocktail party effect. There are many factors that influence this effect. Despite its importance, it is still unclear as to how auditory spatial attention distinguishes a target sound from others. In this study, we investigate how auditory spatial information affects word intelligibility in complex acoustic scenes. To simulate such scenes, a target sound is presented among spatially distributed non-targeted ones. By introducing beforehand, the listener's auditory spatial attention is attracted to a specific loudspeaker from which target speech sounds are presented. This is done to examine how attention causes word intelligibility to increase and how large the spatial extent of the effect is. The results show that word intelligibility increases approximately 15% when the target sound is presented from a specific direction. Furthermore, word intelligibility decreases as the angular distance from the specific direction increases. This pattern shows the spread of the effects of auditory spatial attention.