PURPOSE: To provide a transformer and an assembling method in which the occurrence of defective terminal part and insufficient contact between a wire side terminal and a transformer side terminal can be prevented at the time of connecting the wire side terminal at terminal section and the transformer side terminal at transformer section.

CONSTITUTION: The transformer comprises a transformer section 20 including a coil 22 and terminals 23, 23 connected therewith, and a terminal section 40 being fixed the transformer section 20 while including quick terminals 42, 42 to be connected with the core 1A of a wire 1. The quick terminals 42, 42 at the terminal section 40 are provided, at the part to be fixed to the connection terminals 23, 23, with tongues 42F, 42F for receiving the connection terminals 23, 23.