Atelier Z is a Tokyo-based builder of electric basses, guitars, and upright basses founded in 1988 by Kokichi "Johnny" Motohashi. The brand emerged from DAY'S Corporation and became known for custom-shop Japanese craftsmanship, with much of its early development shaped through collaborations with session and studio bassists. In 2019, the company reorganized under the name ATELIER Z Guitar Works.

The brand is best known for its J-style and P/J-style four- and five-string basses, with flagship lines including the M#245, M#265, Beta, and ZPO models. Instruments typically feature active preamps, bolt-on construction, and a punchy, articulate voicing that is often associated with Japanese slap and fingerstyle playing. Alongside the bass lineup, Atelier Z produces electric guitars, upright/hybrid basses (URB/CUB), and a range of outboard preamps and boost pedals developed from their onboard electronics.

Atelier Z has a strong following among Japanese session and touring bassists and has also been embraced internationally through dealers such as Bass Japan Direct. The instruments are hand-built in Tokyo and the company also operates a custom-order and repair workshop.

Atelier Z has 8 products cataloged on Equipboard, including Electric Basses. Their gear is featured by 6 artists, with the strongest followings in Rock, Metal, and Pop. Notable users include Jerry Barnes, KenKen, and Bohte "BOH" Saisuke.