A fastener wherein right and left side edge portions can be engaged using a magnetic force, and which can be applied preferably for plastic article such as clothes and further prevented from being opened carelessly even if a lateral pulling force is applied when right and left elements are engaged. In the fastener, a plurality of first and second magnetic elements(3A,3B) having magnetism are provided in lines on a pair of first and second fastener tapes(3A,3B), the first and second magnetic elements(3A,3B) are adsorbed to each other using a magnetic force, characterized in that the first and second magnetic elements have head portions(7), a leg portion(8), and engagement / disengagement portions(9,10) formed at the head portions and mechanically engaged with or disengaged from each other between the first and second magnetic elements(3A,3B), the first and second magnetic elements are respectively disposed at predetermined intervals, the magnetic elements(3A) of one fastener tape(2A)(3B) are adsorbed to spaces between the adjacent magnetic elements of the other fastener tape(2B), and the first and second magnetic elements(3A,3B) are engaged with each other alternately.