To provide a connection structure for an electronic circuit unit and an electric connection box capable of improving assembling by reducing a fitting force of an each connection terminal of an electronic circuit unit to a connector for connecting each unit of an electrical connection box and capable of preventing destruction of the connection terminal on the side of the connector for connecting the unit.

In plural connection terminals 11, 12 arranged in two lines in an electronic circuit unit 10, the connection terminals 11, 11... in one of the lines are used for the electric connection to the inside of an electric connection box 20 while the connection terminals 12, 12... of the other line are used for the electrical connection to a wire harness 30. Further in connectors for connecting units 22, 24 which are arranged in two lines, the connector in the other line is a cassette type separated connector 24 for the electrical connection to the wire harness 30. The separated connector 24 is adapted to be freely mounted in and demounted from a connector fitting part 21a which is provided on an electric connection box 20.