A shelf unit, comprising: a first shelf part; a second shelf part configured to slidably couple with the first shelf part and comprising a pair of protrusions protruding at both sides of the second shelf part; and a support part configured to be installed in a storage compartment (11,12) to slidably support the first shelf part and rotatably support the second shelf part, wherein the support part is configured such that the pair of protrusions is selectively coupled and separated between an upper surface and a lower surface of the support part, characterized in that the pair of protrusions is coupled with a pair of protrusion receiving grooves formed between the upper surface and the lower surface of the support part and configured to prevent the pair of protrusions from being separated upward with respect to the support part, and wherein the support part further includes: a pair of protrusion guide grooves configured to guide the pair of protrusions from the lower surface of the support part to the protrusion receiving grooves; and a pair of anti-separation parts configured to be elastically disposed on the pair of protrusion guide grooves so that the pair of protrusions is selectively coupled with and separated from the pair of protrusion receiving grooves, and wherein the pair of protrusion guide grooves includes: a first guide section configured to extend toward the upper surface of the support part from the lower surface of the support part; and a second guide section formed to be inclined downward in a forward or backward direction and configured to connect one end of the first guide section to one side of the pair of protrusion receiving grooves. a first shelf part; a second shelf part configured to slidably couple with the first shelf part and comprising a pair of protrusions protruding at both sides of the second shelf part; and a support part configured to be installed in a storage compartment (11,12) to slidably support the first shelf part and rotatably support the second shelf part, wherein the support part is configured such that the pair of protrusions is selectively coupled and separated between an upper surface and a lower surface of the support part, characterized in that the pair of protrusions is coupled with a pair of protrusion receiving grooves formed between the upper surface and the lower surface of the support part and configured to prevent the pair of protrusions from being separated upward with respect to the support part, and wherein the support part further includes: a pair of protrusion guide grooves configured to guide the pair of protrusions from the lower surface of the support part to the protrusion receiving grooves; and a pair of anti-separation parts configured to be elastically disposed on the pair of protrusion guide grooves so that the pair of protrusions is selectively coupled with and separated from the pair of protrusion receiving grooves, and a pair of protrusion guide grooves configured to guide the pair of protrusions from the lower surface of the support part to the protrusion receiving grooves; and a pair of anti-separation parts configured to be elastically disposed on the pair of protrusion guide grooves so that the pair of protrusions is selectively coupled with and separated from the pair of protrusion receiving grooves, and wherein the pair of protrusion guide grooves includes: a first guide section configured to extend toward the upper surface of the support part from the lower surface of the support part; and a second guide section formed to be inclined downward in a forward or backward direction and configured to connect one end of the first guide section to one side of the pair of protrusion receiving grooves. a first guide section configured to extend toward the upper surface of the support part from the lower surface of the support part; and a second guide section formed to be inclined downward in a forward or backward direction and configured to connect one end of the first guide section to one side of the pair of protrusion receiving grooves.