A pneumatic tire comprising: a tread portion provided with a pair of circumferentially and continuously extending crown main grooves each of which is arranged on each side of the tire equator, a pair of circumferentially and continuously extending shoulder main grooves each of which is arranged axially outside of the crown main groove on each side of the tire equator, and a pair of middle land portions each of which is arranged between the crown main groove and the shoulder main groove on each side of the tire equator; each of the middle land porti ons provided with a plurality of middle sipes each having an axially inner end communicated with the crown main groove and an axially outer end communicated with the shoulder main groove, and a middle sub-groove extending between circumferentially adjacent middle sipes without intersecting with the middle sipes; each of the middle sipes extending in an arc-like shape such that an angle (θ1) with respect to the circumferential direction of the tire gradually increases from its inner end toward its outer end; a circumferential length from the outer end to the inner end of the middle sipe being in a range of from 0.6 to 1.0 times an arrangement pitch of the middle sipes; the middle sub-groove having an axially outer end communicating with the shoulder main groove and an axially inner end terminating without communicating with the crown main groove; the middle sub-groove extending in an arc-like shape such that an angle (θ2) with respect to the circumferential direction of the tire gradually increases from its inner end toward its outer end; a circumferential length from the outer end to the inner end of the middle sub-groove being smaller than the circumferential length of the middle sipe; and the circumferentially adjacent middle sipe and middle sub-groove overlapping one another in the axial direction of the tire, characterized in that the crown main grooves have both groove edges extending in a linear fashion, the shoulder main grooves have both groove edges extending in a linear fashion, and that the groove widths of the shoulder main grooves are larger than the groove widths of the crown main grooves. a tread portion provided with a pair of circumferentially and continuously extending crown main grooves each of which is arranged on each side of the tire equator, a pair of circumferentially and continuously extending shoulder main grooves each of which is arranged axially outside of the crown main groove on each side of the tire equator, and a pair of middle land portions each of which is arranged between the crown main groove and the shoulder main groove on each side of the tire equator; each of the middle land porti ons provided with a plurality of middle sipes each having an axially inner end communicated with the crown main groove and an axially outer end communicated with the shoulder main groove, and a middle sub-groove extending between circumferentially adjacent middle sipes without intersecting with the middle sipes; each of the middle sipes extending in an arc-like shape such that an angle (θ1) with respect to the circumferential direction of the tire gradually increases from its inner end toward its outer end; a circumferential length from the outer end to the inner end of the middle sipe being in a range of from 0.6 to 1.0 times an arrangement pitch of the middle sipes; the middle sub-groove having an axially outer end communicating with the shoulder main groove and an axially inner end terminating without communicating with the crown main groove; the middle sub-groove extending in an arc-like shape such that an angle (θ2) with respect to the circumferential direction of the tire gradually increases from its inner end toward its outer end; a circumferential length from the outer end to the inner end of the middle sub-groove being smaller than the circumferential length of the middle sipe; and the circumferentially adjacent middle sipe and middle sub-groove overlapping one another in the axial direction of the tire, characterized in that the crown main grooves have both groove edges extending in a linear fashion, the shoulder main grooves have both groove edges extending in a linear fashion, and that the groove widths of the shoulder main grooves are larger than the groove widths of the crown main grooves.