Abstract: The present invention relates to a transformer having a noise reduction structure. A tank (12) forms the exterior of the transformer (10). An inner space (14) filled with insulating oil is formed inside the tank (12). An iron core (20) is provided inside the tank (12) by a lower frame (16) and an upper frame (18), and coils (22) are wound around parts of the iron core (20) extending in the direction of gravity. An insulating sheet (24) is provided to encompass the surface of each of the coils (22), and has ridge portions (26) and groove portions (28), which are formed to extend in the height direction of the iron core (20). It is preferable that the side surfaces of the groove portions (28) are formed in parallel so as to face each other.