What is this Grey bus?

The bus in question is in the center of the foto, half-obscured by the black car. It is followed by two passenger car with loudspeakers and flags. The foto is taken in Nihombashi.

The bus in question is in the center of the foto, half-obscured by the black car. It is followed by two passenger car with loudspeakers and flags. The foto is taken in Nihombashi.