The Multi-Aperture Spectroscopic Telescope (MAST) is a new telescope array with a novel design, currently being constructed at the Weizmann Astrophysical Observatory in Israel. It comprises twenty 60 cm telescopes, collectively providing the light-gathering power of a single 2.7 m telescope. MAST features two fiber-fed spectrographs with low and high resolutions, covering the optical domain. To remove instrument signatures and calibrate the wavelength, a calibration unit utilizing quartz-tungsten-halogen (QTH) and ThAr lamps to generate arc and flat spectra will be employed. The lamp outputs are homogenized and distributed by a series of beamsplitters into five identical fiber outlets feeding the spectrographs. This presentation outlines the opto-mechanical design of the calibration unit and the development status of the subsystem.