To provide a coil bobbin which has improved insulation between a lead wire and a core and high reliability, and a transformer and a cholk coil using the same.

A terminal block 7 is provided with a plurality of pins 1 and 2 erected in the planary and vertical directions of the terminal block 7. When the plane direction of the terminal block 7 is defined as an XY plane direction, arrangement direction of the pins as a Y direction, and the lengthwise direction of the pins as a Z direction, respectively, a first groove 5 with a U-shaped cross section penetrating in the Z direction is provided within a space between the sealed parts of two pins on the terminal block 7, and a first step 3 wherein a space open part is formed in the Z direction and the XY plane forms a bottom surface is provided adjacent to the groove 5, and then a second groove 6 with a U-shaped cross section penetrating in the Y direction is provided over the step 3 adjacent to the sealed part of the pin 2 near the first step 3. Furthermore, a second step 4 is provided adjacent to the sealed part of the pin 2.