Device for folding and unfolding hail protection nets in crop fields which comprises: - a support structure formed by a series of posts fixed to the ground in rows in correspondence with the crops, - a set of hail-retaining protection nets or mesh, adapted to cover the crop field, joined to the rows of posts by means of upper ancillary fixed cables or ridge cables that extend joining the upper parts of the posts that constitute each row and which have shackles or rings evenly distributed along the entire length thereof, to which the net is joined, - main horizontal shaft pulleys, disposed in pairs on the sides of the upper part of the posts of the initial and final ends of each row, wherethrough corresponding locked-coil main cables run, - a second lower ancillary fixed cable that extends along the posts of each row, disposed at a height lower than that of the locked-coil main cables, said ancillary fixed cable also being equipped with second shackles or rings evenly distributed along the entire length thereof, and - net deployment cables fixed to attachment points evenly distributed along the lateral ends of said net that extend, from said attachment point, towards the adjacent row, being the device characterized in that - the deployment cables pass through the rings of the lower ancillary fixed cable to return to their row and connect to the lower section of the locked-coil main cable of their row, and in that - the device further comprises net retraction cables fixed to the same net attachment points as the deployment cables, which pass, from said attachment point, through the rings of the lower ancillary fixed cable of their own row to connect to the upper section of the locked-coil main cable of their own row. - a support structure formed by a series of posts fixed to the ground in rows in correspondence with the crops, - a set of hail-retaining protection nets or mesh, adapted to cover the crop field, joined to the rows of posts by means of upper ancillary fixed cables or ridge cables that extend joining the upper parts of the posts that constitute each row and which have shackles or rings evenly distributed along the entire length thereof, to which the net is joined, - main horizontal shaft pulleys, disposed in pairs on the sides of the upper part of the posts of the initial and final ends of each row, wherethrough corresponding locked-coil main cables run, - a second lower ancillary fixed cable that extends along the posts of each row, disposed at a height lower than that of the locked-coil main cables, said ancillary fixed cable also being equipped with second shackles or rings evenly distributed along the entire length thereof, and - net deployment cables fixed to attachment points evenly distributed along the lateral ends of said net that extend, from said attachment point, towards the adjacent row, - the deployment cables pass through the rings of the lower ancillary fixed cable to return to their row and connect to the lower section of the locked-coil main cable of their row, and in that - the device further comprises net retraction cables fixed to the same net attachment points as the deployment cables, which pass, from said attachment point, through the rings of the lower ancillary fixed cable of their own row to connect to the upper section of the locked-coil main cable of their own row.