A transformer capable of maintaining its height is provided. The transformer is formed on a circuit board having a receiving hole. The transformer comprises a winding module, two magnetic core modules contacting and holding the winding module, a plurality of pins and at least one supporting means. The winding module comprises a winding baseboard and a winding pillar where a winding structure is formed thereon. The winding pillar is received in the receiving hole. Each of the pins comprises a first bent part separating the corresponding pin into a first portion connected to the winding baseboard and a second portion connected to the circuit board around the receiving hole. The supporting means is formed between the first portion of at least one of the pins and the circuit board to contact the first portion and the circuit board to maintain the distance between them.