A turbocharger for supercharging an internal combustion engine, comprising: a bearing housing which accommodates a bearing supporting a rotational shaft of the turbocharger; an oil discharge port for discharging lubricant oil stored in an internal space of the bearing housing; an oil discharge pipe connected to the oil discharge port; an air pocket formed in the oil discharge port or the oil discharge pipe; and a communication flow passage which brings the air pocket and the internal space into communication, the turbocharger characterized in that the communication flow passage is formed: (i) as a through hole formed by making a hole on the bearing housing, and extends along the inner wall of the oil discharge port, the turbocharger comprising: an insert member inserted into the internal space; and a seal member disposed along a circumferential direction of the rotational shaft to seal a gap between the insert member and the bearing housing, wherein the communication flow passage is in communication with the internal space from above, via a seal groove formed on the bearing housing to accommodate the seal member, and wherein the insert member has a through groove which brings the seal groove and the internal space into communication, or (ii) by engaging a flow-passage forming portion which extends upward from the oil discharge port with the inner wall surface of the bearing housing with an attachment member mounted to the oil discharge port and including a canopy portion, so that a diameter of the oil discharge port is smaller than that of a most upstream portion of the oil discharge pipe, wherein the air pocket is formed by a step formed between the attachment member and the most upstream portion. a bearing housing which accommodates a bearing supporting a rotational shaft of the turbocharger; an oil discharge port for discharging lubricant oil stored in an internal space of the bearing housing; an oil discharge pipe connected to the oil discharge port; an air pocket formed in the oil discharge port or the oil discharge pipe; and a communication flow passage which brings the air pocket and the internal space into communication, the turbocharger characterized in that the communication flow passage is formed: (i) as a through hole formed by making a hole on the bearing housing, and extends along the inner wall of the oil discharge port, the turbocharger comprising: an insert member inserted into the internal space; and a seal member disposed along a circumferential direction of the rotational shaft to seal a gap between the insert member and the bearing housing, wherein the communication flow passage is in communication with the internal space from above, via a seal groove formed on the bearing housing to accommodate the seal member, and wherein the insert member has a through groove which brings the seal groove and the internal space into communication, or (ii) by engaging a flow-passage forming portion which extends upward from the oil discharge port with the inner wall surface of the bearing housing with an attachment member mounted to the oil discharge port and including a canopy portion, so that a diameter of the oil discharge port is smaller than that of a most upstream portion of the oil discharge pipe, (i) as a through hole formed by making a hole on the bearing housing, and extends along the inner wall of the oil discharge port, the turbocharger comprising: an insert member inserted into the internal space; and a seal member disposed along a circumferential direction of the rotational shaft to seal a gap between the insert member and the bearing housing, wherein the communication flow passage is in communication with the internal space from above, via a seal groove formed on the bearing housing to accommodate the seal member, and wherein the insert member has a through groove which brings the seal groove and the internal space into communication, or an insert member inserted into the internal space; and a seal member disposed along a circumferential direction of the rotational shaft to seal a gap between the insert member and the bearing housing, wherein the communication flow passage is in communication with the internal space from above, via a seal groove formed on the bearing housing to accommodate the seal member, and wherein the insert member has a through groove which brings the seal groove and the internal space into communication, or (ii) by engaging a flow-passage forming portion which extends upward from the oil discharge port with the inner wall surface of the bearing housing with an attachment member mounted to the oil discharge port and including a canopy portion, so that a diameter of the oil discharge port is smaller than that of a most upstream portion of the oil discharge pipe, wherein the air pocket is formed by a step formed between the attachment member and the most upstream portion.