A pneumatic tire, comprising: a plurality of land portions (18, 24) that are provided at a tread and that are partitioned by a plurality of circumferential direction grooves (14, 16) that extend along a tire circumferential direction; a lug groove that is provided at at least one land portion among the plurality of land portions (18, 24) and that crosses the land portion in a tire width direction; a fine groove that is provided at a groove bottom portion of the lug groove, that has a narrower groove width than the lug groove, and that has a groove bottom face formed with a circular arc shaped profile when viewed in cross-section at right angles to a groove length direction; characterised in that said pneumatic tire further comprises: a first curved face that is provided so as to couple one of mutually facing groove side faces of the lug groove to a groove side face of the respective circumferential direction groove, and that extends toward a groove bottom face of the circumferential direction grooves (14, 16); and a second curved face that is provided so as to couple another of the mutually facing groove side faces of the lug groove to the groove side face of the respective circumferential direction groove, and that extends toward the groove bottom face of the circumferential direction grooves (14, 16), wherein a length direction end portion of one groove side face of the fine groove is smoothly connected to the first curved face by a first coupling curved face, and a length direction end portion of the other groove side face of the fine groove is smoothly coupled to the second curved face by a second coupling curved face; and a third coupling curved face (31, 33) joins the groove bottom face at a length direction end portion of the fine groove, to a groove side face of the circumferential direction grooves. a plurality of land portions (18, 24) that are provided at a tread and that are partitioned by a plurality of circumferential direction grooves (14, 16) that extend along a tire circumferential direction; a lug groove that is provided at at least one land portion among the plurality of land portions (18, 24) and that crosses the land portion in a tire width direction; a fine groove that is provided at a groove bottom portion of the lug groove, that has a narrower groove width than the lug groove, and that has a groove bottom face formed with a circular arc shaped profile when viewed in cross-section at right angles to a groove length direction; characterised in that said pneumatic tire further comprises: a first curved face that is provided so as to couple one of mutually facing groove side faces of the lug groove to a groove side face of the respective circumferential direction groove, and that extends toward a groove bottom face of the circumferential direction grooves (14, 16); and a second curved face that is provided so as to couple another of the mutually facing groove side faces of the lug groove to the groove side face of the respective circumferential direction groove, and that extends toward the groove bottom face of the circumferential direction grooves (14, 16), wherein a length direction end portion of one groove side face of the fine groove is smoothly connected to the first curved face by a first coupling curved face, and a length direction end portion of the other groove side face of the fine groove is smoothly coupled to the second curved face by a second coupling curved face; and a third coupling curved face (31, 33) joins the groove bottom face at a length direction end portion of the fine groove, to a groove side face of the circumferential direction grooves. a first curved face that is provided so as to couple one of mutually facing groove side faces of the lug groove to a groove side face of the respective circumferential direction groove, and that extends toward a groove bottom face of the circumferential direction grooves (14, 16); and a second curved face that is provided so as to couple another of the mutually facing groove side faces of the lug groove to the groove side face of the respective circumferential direction groove, and that extends toward the groove bottom face of the circumferential direction grooves (14, 16), wherein a length direction end portion of one groove side face of the fine groove is smoothly connected to the first curved face by a first coupling curved face, and a length direction end portion of the other groove side face of the fine groove is smoothly coupled to the second curved face by a second coupling curved face; and a third coupling curved face (31, 33) joins the groove bottom face at a length direction end portion of the fine groove, to a groove side face of the circumferential direction grooves.