Going off the model number, it would seem to be an
Apple part. If it is
all the same color beige (button isn't a slightly darker color), then I
would think it is the original Apple II mouse (which would fit with the
model number designator A2M for Apple 2 Mouse)
The leading A2 certainly means it's an Apple product relating to the
Apple II family, but the M doesn't make it a mouse. Lots of things
were A2Mxxxx, and only a tiny number were mice.