A solar cell module retaining structure for fastening a solar cell module to a supporting member, wherein the solar cell module includes a solar cell panel body whose shape is flat and constituted by a plurality of edges, the solar cell panel body including a solar cell and frames to be fastened to at least one pair of facing edges of the solar cell panel bodies adjacent to each other, and whereby, the solar cell module is capable of being fastened to the supporting member by connecting each of holding members to the frames fastened respectively to the pair of facing edges of the solar cell panel bodies adjacent to each other, and by fastening each holding member to the supporting member, wherein each of the holding members is slidable relative to the frames and: connects the two solar cell modules arranged in an extending direction of the supporting member such that the frames of the solar cell panel bodies of the two solar cell modules are adjacent to each other, and such that the two solar cell modules make substantially a flush surface; and wherein each of the holding members further restricts movement of one of the two solar cell modules in a direction perpendicular to an extending direction of the frames; and is fastened to the supporting member below the other of the two solar cell modules, and wherein the frame, configured to extend in a longitudinal direction while having the same cross-section in a longitudinal direction, comprises: a C-shaped insertion support portion having an opening of the C-shape at one side, the edge of the solar cell panel body capable of being inserted into the C-shaped insertion support portion, and supported by the C-shaped insertion support portion; a connection portion arranged below the C-shaped insertion support portion and having an opening at the other side opposite to the one side; and an engagement protrusion arranged below the connection portion and having an opening at the other side, an end portion of the engagement protrusion projecting upward, and the holding member, configured to be shorter than the frame in a longitudinal direction while having the same cross-section in a longitudinal direction, the holding member further comprising: a pair of connecting portions capable of being inserted in the connection portion and extending in a direction away from each other; a down section extending downward from the pair of the connecting portions; a seat section arranged at the lower end of the down section and capable of having a bottom of the frame mounted thereon; an engagement piece arranged on the down section between the seat section and the connecting portion, and extending from the down section in the same direction as a direction of the connecting portion, the engagement piece having an engagement protrusion portion projecting downward so as to engage the engagement protrusion of the frame; and a holding portion having a bottom surface on the same surface as a bottom surface of the seat section and extending in a direction opposite to a direction of the engagement piece so as to be fastened to the supporting member. a C-shaped insertion support portion having an opening of the C-shape at one side, the edge of the solar cell panel body capable of being inserted into the C-shaped insertion support portion, and supported by the C-shaped insertion support portion; a connection portion arranged below the C-shaped insertion support portion and having an opening at the other side opposite to the one side; and an engagement protrusion arranged below the connection portion and having an opening at the other side, an end portion of the engagement protrusion projecting upward, and the holding member, configured to be shorter than the frame in a longitudinal direction while having the same cross-section in a longitudinal direction, the holding member further comprising: a pair of connecting portions capable of being inserted in the connection portion and extending in a direction away from each other; a down section extending downward from the pair of the connecting portions; a seat section arranged at the lower end of the down section and capable of having a bottom of the frame mounted thereon; an engagement piece arranged on the down section between the seat section and the connecting portion, and extending from the down section in the same direction as a direction of the connecting portion, the engagement piece having an engagement protrusion portion projecting downward so as to engage the engagement protrusion of the frame; and a holding portion having a bottom surface on the same surface as a bottom surface of the seat section and extending in a direction opposite to a direction of the engagement piece so as to be fastened to the supporting member. a pair of connecting portions capable of being inserted in the connection portion and extending in a direction away from each other; a down section extending downward from the pair of the connecting portions; a seat section arranged at the lower end of the down section and capable of having a bottom of the frame mounted thereon; an engagement piece arranged on the down section between the seat section and the connecting portion, and extending from the down section in the same direction as a direction of the connecting portion, the engagement piece having an engagement protrusion portion projecting downward so as to engage the engagement protrusion of the frame; and a holding portion having a bottom surface on the same surface as a bottom surface of the seat section and extending in a direction opposite to a direction of the engagement piece so as to be fastened to the supporting member.