The Casio Casiotone MT-40 is an electronic keyboard, formerly produced by Casio and originally developed for the consumer market. It has 37 main keys and 15 smaller bass keys, with 9-voice polyphony: eight notes may be played on the main keys, and one note on the bass. The bass section has one timbre, and the main section has 22, assignable to one of four presets. Like most small Casio keyboards, it also has a drum section with 6 different beats, a tempo knob, and a "fill" button. The fill button plays sixteenth note pulses of either the "snare" or "kick" as long as it is held down. Production started in the early 1980s and ceased shortly thereafter. The successor of the MT-40 came with a gray case, and was sold as the MT-41.
Brazilian/British composer Ritchie used the Casio MT-30 in his Brazil soap soundtrack Menina Veneno (1982).
Composer Ralph Jones used the Casio MT-30 with cymbals and crystal glasses in his score to Amy Holden Jones' 1982 horror film The Slumber Party Massacre.
The MT-40 had a built-in pattern widely reputed to be based either on the Eddie Cochran song "Somethin' Else", or the Sex Pistols' "Anarchy in the UK". The pattern's creator, Casio's Product Development and Music Engineer Hiroko Okuda, has denied either source, saying instead that it was based on a 1970s British rock song she declined to identify. Some have suggested the song may be David Bowie's "Hang On to Yourself".
A synthesizer version of the song's bassline was used as the basis of one of the most popular dancehall music riddims of Jamaican music: the Sleng Teng riddim, which started the "digital reggae" revolution in 1985.
The MT-40 has secured a niche in indie music. It is used in some songs by the Magnetic Fields, and is featured prominently on most of Emperor X's album Tectonic Membrane/Thin Strip on an Edgeless Platform. Its thin fuzz can be heard on lesser known Australian indie band Turnstyle's top 20 single "Spray Water on the Stereo". California-based indie rock group Picture Atlantic used a mixture of the MT-40's organ sound and bass notes for their tracks "Circe", "Anytime/Coats of Armor", and "....That's Just Me" on their album Kleos. San Francisco indie rock duo Casy and Brian exclusively used the Casio MT-40 for three of their four releases, altering its sound with effects such as overdrive pedals to accompany drums. Former Boston/San Francisco street musician, The Space Lady, plays the MT-40 through a Small Stone phase shifter to create a spacey, ethereal tone to accompany her delay-enhanced vocals. In the UK, the Farmer's Boys, recording for EMI and acclaimed by John Peel, used it on a number of singles and album tracks—with an ironing board as a keyboard stand. In 2015, Japanese musician Tentenko (formerly of BiS) released an album recorded using the keyboard as the only accompanying instrument.