Abstract: A multi-junction solar cell is provided and includes: a first solar cell element, having a first band gap and transmitting a part of incident light; a first conductive film, formed on a back surface of the first solar cell element and having light transmissivity and conductivity; a second solar cell element, having a second band gap smaller than the first band gap; a second conductive film, formed on a front surface of the second solar cell element and having light transmissivity and conductivity; and an adhesion layer, joining surfaces of the first and second conductive films, and having light transmissivity and conductivity. When refractive indexes of the first solar cell element, the first conductive film, the second solar cell element, the second conductive film and the adhesion layer are n1, n2, n3, n4 and n5, respectively, relations of n1>n2>n5 and n3>n4>n5 are satisfied.