A refrigerator comprising: a main body having a front side and a rear side; a storage chamber (50, 60) provided in the main body and having an opening at the front side of the main body; a sliding door for opening or closing the opening of the storage chamber; a storage basket to be drawn into or out of the storage chamber by being moved together with the sliding door, the storage basket having first and second side walls (250a,b) each having a coupling wall with a coupling surface facing down and a protrusion protruding from the coupling surface; first and second rail units each disposed between the storage basket and the main body and supporting the sliding door, the first and second rail unit each having a hole into which the protrusions of the storage basket are inserted, wherein an auxiliary basket is provided vertically on top of the storage basket and supported by the storage basket, configured to be drawn into or out on an upper portion of the storage basket, and having a roller to perform a rolling motion, the storage basket includes: a front protrusion on an upper portion of the first sidewall, the front protrusion protruding upward, a rear protrusion on the upper portion of the first sidewall, the rear protrusion protruding upward, a roller support surface provided on a top surface of the first sidewall, the roller support surface extending from the front protrusion to the rear protrusion to support the roller with the front protrusion restricting forward movement of the roller and the rear protrusion restricting backward movement of the roller, and a roller support guide extending along a side of the roller support surface to guide the roller. a main body having a front side and a rear side; a storage chamber (50, 60) provided in the main body and having an opening at the front side of the main body; a sliding door for opening or closing the opening of the storage chamber; a storage basket to be drawn into or out of the storage chamber by being moved together with the sliding door, the storage basket having first and second side walls (250a,b) each having a coupling wall with a coupling surface facing down and a protrusion protruding from the coupling surface; first and second rail units each disposed between the storage basket and the main body and supporting the sliding door, the first and second rail unit each having a hole into which the protrusions of the storage basket are inserted, wherein an auxiliary basket is provided vertically on top of the storage basket and supported by the storage basket, configured to be drawn into or out on an upper portion of the storage basket, and having a roller to perform a rolling motion, the storage basket includes: a front protrusion on an upper portion of the first sidewall, the front protrusion protruding upward, a rear protrusion on the upper portion of the first sidewall, the rear protrusion protruding upward, a roller support surface provided on a top surface of the first sidewall, the roller support surface extending from the front protrusion to the rear protrusion to support the roller with the front protrusion restricting forward movement of the roller and the rear protrusion restricting backward movement of the roller, and a roller support guide extending along a side of the roller support surface to guide the roller. a front protrusion on an upper portion of the first sidewall, the front protrusion protruding upward, a rear protrusion on the upper portion of the first sidewall, the rear protrusion protruding upward, a roller support surface provided on a top surface of the first sidewall, the roller support surface extending from the front protrusion to the rear protrusion to support the roller with the front protrusion restricting forward movement of the roller and the rear protrusion restricting backward movement of the roller, and a roller support guide extending along a side of the roller support surface to guide the roller.