To enable accurate judgement of failure and the like in a speaker(s) for guests through a monitor speaker in a driver space even in case of disconnection in the side of speaker for the guests or failure in the speaker.

In a monitor speaker device for buses wherein a floor surface 4 for guests is set higher in its height through a second step than a floor surface 3 of driver's seat being continuous to a getting on/off part through a first step 2, and a plurality of speakers 6 for the guests are arranged at a specified distance in a luggage shelf 8 formed at a ceiling shoulder part of a gest room in the lengthwise direction of a bus, a monitor speaker 11 connected to a guest speaker 6 in series is arranged in the vicinity of audio equipment 9D of instrument pannel 9 positioned ahead of the driver's seat floor surface 3.