A transformer comprising: a frame type iron core comprising first and second plate-shaped magnetic members (101; 102-106), wherein each first plate-shaped magnetic member comprises three or more stacked magnetic member units (101 a, 101 b, 101 c) and each second plate-shaped member (102 - 106) comprises two stacked magnetic member units (102a, 102b), and wherein the first and second plate-shaped magnetic members have openings (P1, P2) and are laminated onto one another such as to form respective annular magnetic circuits in the frame type iron core, wherein each of the first plate-shaped magnetic members has a first width (W1a, W1b) in a direction perpendicular to the lamination direction and the second plate-shaped magnetic members have corresponding second widths (W2a, W2b, W3a, W3b, W4a, W4b, W5a, W5b, W6a, W6b) different from the first width, and wherein the first and second plate-shaped magnetic members are laminated onto one another in the order based on their respective first and second widths, the first width (W1a, W1b) being the largest width of the first and second widths in the frame type iron core, wherein each of the magnetic member units (101 a, 101b, 101c; 102a, 102b) of the first and second plate-shaped magnetic members comprises magnetic member pieces (1011-1015; 1021, 1023; A, B, C, D, E) forming respective side portions of the plate-shaped magnetic member along the corresponding annular magnetic circuit, the magnetic member pieces being joined to each other at respective end surfaces (S A, S D), each adjacent pair of joined end surfaces forming a joint portion (J1, J2, J3, J4) at a corresponding corner portion (a-f) of the magnetic member units (101 a, 101b, 101c; 102a, 102b) of the first and second plate-shaped magnetic members, and wherein a coil (20a-c) wound around a part of the frame type iron core is adapted to excite the frame type iron core and to generate a magnetic flux in the frame type iron core, when electricity is conducted through the coil; characterized in that there are three or more joint portions (101aj, 101bj, 101cj, 101dj) formed at each corner portion (a, b, c, d, e, f) of the magnetic member units (101 a, 101b, 101c) of the plate-shaped magnetic members and shifted from each other by respective first distances (d 101A, d 101B) in the direction of the magnetic path formed by the first plate-shaped member and there are two joint portions (102aj, 102bj, 102cj, 102dj) formed at each corner portion of each of the magnetic member units (102a, 102b) of the second plate-shaped magnetic members (102, 103, 104, 105, 106) and shifted from each other by respective second distances (d 102) in the direction of the magnetic path formed by the second plate-shaped member and each of the second distances (d 102) larger than any one of the first distances (d 101A, d 101B). a frame type iron core comprising first and second plate-shaped magnetic members (101; 102-106), wherein each first plate-shaped magnetic member comprises three or more stacked magnetic member units (101 a, 101 b, 101 c) and each second plate-shaped member (102 - 106) comprises two stacked magnetic member units (102a, 102b), and wherein the first and second plate-shaped magnetic members have openings (P1, P2) and are laminated onto one another such as to form respective annular magnetic circuits in the frame type iron core, wherein each of the first plate-shaped magnetic members has a first width (W1a, W1b) in a direction perpendicular to the lamination direction and the second plate-shaped magnetic members have corresponding second widths (W2a, W2b, W3a, W3b, W4a, W4b, W5a, W5b, W6a, W6b) different from the first width, and wherein the first and second plate-shaped magnetic members are laminated onto one another in the order based on their respective first and second widths, the first width (W1a, W1b) being the largest width of the first and second widths in the frame type iron core, wherein each of the magnetic member units (101 a, 101b, 101c; 102a, 102b) of the first and second plate-shaped magnetic members comprises magnetic member pieces (1011-1015; 1021, 1023; A, B, C, D, E) forming respective side portions of the plate-shaped magnetic member along the corresponding annular magnetic circuit, the magnetic member pieces being joined to each other at respective end surfaces (S A, S D), each adjacent pair of joined end surfaces forming a joint portion (J1, J2, J3, J4) at a corresponding corner portion (a-f) of the magnetic member units (101 a, 101b, 101c; 102a, 102b) of the first and second plate-shaped magnetic members, and wherein a coil (20a-c) wound around a part of the frame type iron core is adapted to excite the frame type iron core and to generate a magnetic flux in the frame type iron core, when electricity is conducted through the coil; characterized in that there are three or more joint portions (101aj, 101bj, 101cj, 101dj) formed at each corner portion (a, b, c, d, e, f) of the magnetic member units (101 a, 101b, 101c) of the plate-shaped magnetic members and shifted from each other by respective first distances (d 101A, d 101B) in the direction of the magnetic path formed by the first plate-shaped member and there are two joint portions (102aj, 102bj, 102cj, 102dj) formed at each corner portion of each of the magnetic member units (102a, 102b) of the second plate-shaped magnetic members (102, 103, 104, 105, 106) and shifted from each other by respective second distances (d 102) in the direction of the magnetic path formed by the second plate-shaped member and each of the second distances (d 102) larger than any one of the first distances (d 101A, d 101B).