An electrical connection box is provided with a connector-attached board and a shield case that internally houses the connector-attached board. The connector-attached board is provided with a circuit board, a connector that is fixed to the circuit board and that engages with a mating connector, and an attachment that is attached to the connector. The shield case surrounds the circuit board and is provided with an upper short wall portion and a lower short wall portion that include a connector opening for facing the connector outside. The attachment is provided with a waterproof portion that covers the periphery of an engagement surface of the connector that faces the mating connector, and the waterproof portion is provided with a waterproof wall that covers the periphery of the connector and the mating connector.