1. A position detecting device comprising: a storage unit that stores therein sound source information including: identification information assigned to each sound source that can be visually and auditorily identified, image processing information including an image processing procedure for visually identifying sound sources and visual feature information indicative of visual features of the sound sources, sound processing information including a sound processing procedure for auditorily identifying the sound sources and auditory feature information indicative of auditory features of the sound sources, and a plurality of pieces of detection strategy information indicative of which one or both of the image processing information and the sound processing information is to be used to detect the sound sources; an image acquiring unit that acquires an image of the sound sources; a sound collecting unit that collects sound produced by the sound sources; a visual-feature detecting unit that detects a visual feature of a sound source by performing the image processing procedure based on the image acquired by the image acquiring unit and the image processing information, detects a first position of the sound source from the visual feature, and outputs visually localizing information indicative of the first position of the sound source; an auditory-feature detecting unit that detects an auditory feature of the sound source by performing the sound processing procedure based on the sound collected by the sound collecting unit and the sound processing information, detects a second position of the sound source based on the auditory feature, and outputs auditorily localizing information indicative of the second position of the sound source; and a sound-source detecting unit that controls the visual-feature detecting unit and the auditory-feature detecting unit based on the detection strategy information, and detects a third position of the sound source based on the visually localizing information output from the visual-feature detecting unit and the auditorily localizing information output from the auditory-feature detecting unit.