An optical module includes a circuit board having a through hole for the lead terminal, a signal wiring connected to the lead terminal, a ground layer providing a reference potential, an opening through which the ground layer is exposed, and a bonding material connecting the ground layer to the metallic base. The lead terminal extends in a first direction, and the circuit board and the signal wiring extend in a second direction. When the circuit board is viewed from the first direction, the opening overlaps with the signal wiring, or when the opening does not overlap with the signal wiring, a first distance between the signal wiring and a closest point of the opening to the signal wiring is smaller than a second distance between the closest point and an edge of the circuit board.