Transformer and radio frequency module

A transformer comprising:

• a balanced side coil that has a first end, a second end, and an intermediate tap included between the first end and the second end;
• an unbalanced side coil that has a third end and a fourth end, the fourth end being grounded;
• an external connection wiring pattern portion that is electrically connected to the intermediate tap;
• and
• a multilayer substrate that has a plurality of dielectric layers, wherein
• the balanced side coil, the unbalanced side coil, and the wiring pattern portion are disposed on dielectric layers different from each other in the plurality of dielectric layers of the multilayer substrate,
• the balanced side coil and the unbalanced side coil at least partially overlap each other in a plan view from a thickness direction of the multilayer substrate, and
• the wiring pattern portion has an overlapping portion that overlaps the unbalanced side coil along a peripheral direction in a plan view from the thickness direction of the multilayer substrate.