A device for changing a frame angle of foldable articles including chairs, beds, and tents, the device combining leg frames using a connecting and assembling member and an elastic string and thus makes up a leg or a support frame of the fordable article, the device comprising: the connecting and assembling member with which a first end of the elastic string is combined in a manner to be fixed or to pass through and which has multiple combination grooves each of which has a shape that corresponds to a cross-sectional shape of the leg frame such that the leg frame combined with a second end of the elastic string is selectively combined with the connecting and assembling member in an angle-changing manner at a varying installation angle; the elastic string having the first end that is fixed to or that passes through the connecting and assembling member and the second end that is combined with the leg frame such that the leg frame is elastically operable; and the leg frame that is combined with the first end of the elastic string and that is elastically insertable into or separable from the connecting and assembling member, wherein an opening portion that is a lengthwise-extending hole is formed in the connecting and assembling member, and the connecting and assembling member includes a combination block portion that forms multiple combination grooves (10a, 10b, 10c) by partitioning the opening portion; characterized in that the combination block portion is configured with first and second block pieces (200a, 200b) that are inserted into the opening portion and then are symmetrically combined with the connecting and assembling member, an opening hole through which the elastic string passes is formed between the first and second block pieces (200a, 200b), and multiple combination grooves (10a, 10b, 10c) are formed in both sides of the combination block portion or in the middle thereof. the connecting and assembling member with which a first end of the elastic string is combined in a manner to be fixed or to pass through and which has multiple combination grooves each of which has a shape that corresponds to a cross-sectional shape of the leg frame such that the leg frame combined with a second end of the elastic string is selectively combined with the connecting and assembling member in an angle-changing manner at a varying installation angle; the elastic string having the first end that is fixed to or that passes through the connecting and assembling member and the second end that is combined with the leg frame such that the leg frame is elastically operable; and the leg frame that is combined with the first end of the elastic string and that is elastically insertable into or separable from the connecting and assembling member, wherein an opening portion that is a lengthwise-extending hole is formed in the connecting and assembling member, and the connecting and assembling member includes a combination block portion that forms multiple combination grooves (10a, 10b, 10c) by partitioning the opening portion; characterized in that the combination block portion is configured with first and second block pieces (200a, 200b) that are inserted into the opening portion and then are symmetrically combined with the connecting and assembling member, an opening hole through which the elastic string passes is formed between the first and second block pieces (200a, 200b), and multiple combination grooves (10a, 10b, 10c) are formed in both sides of the combination block portion or in the middle thereof.