The Big-Small Ray Gun looks like a flashlight, so much so that even Arale Norimaki thought it was a flashlight instead. This invention can make any object big or small. Its debut in the manga is in "The Big-Small Gun!" and it later reappears in "Peasuke's First Love," where Arale uses it to make Hiyoko small for Peasuke Soramame. However, she makes her too small. When she is just about to be attacked by a bug, Peasuke saves her with his Peasuke Kick.
Arale and Gatchan play with the Big-Small Ray Gun in "Mammoth Midori: Part 1." Dr. Goat then uses the gun on Senbei, Arale, and Gatchan in "Mammoth Midori: Part 2" to dislodge a deadly mosquito from Midori Yamabuki's body.