A heat exchanger for cooling a target fluid, comprising: an inlet-side tank having an inlet port for leading the target fluid into the inlet-side tank therethrough; an outlet-side tank having an outlet port for leading the target fluid out of the outlet-side tank therethrough; and a plurality of tubes (4A to 4D) each extending from the inlet-side tank to the outlet-side tank, wherein: at least one of the inlet-side tank and the outlet-side tank comprises: a sidewall (6; 9) extending along a given axis (J1; J2) and surrounding the axis; and an end wall (7, 8; 10, 11) closing an opening at an end of the sidewall in a longitudinal direction of the tank along the axis; the plurality of tubes are fixed to the sidewall in a state in which they penetrate through the sidewall via respective ones of a plurality of through-holes formed in the sidewall in such a manner as to be arrayed in a line along the longitudinal direction, the heat exchanger further comprises a protective member fixed to the sidewall to protect a nearest tube (4A, 4D) nearest to the end wall among the plurality of tubes, the protective member having a barrier portion interposed between the end wall and an end portion of the nearest tube disposed inside the sidewall, and the protective member has a covering section extending from a distal end of the barrier portion toward the side away from the end wall, characterized in that the protective member has a pair of fixing sections extending from the covering section, respectively, toward opposite sides in a direction orthogonal to the longitudinal direction of the tank, for fixing the protective member to the sidewall, a small gap is formed between the sidewall and the proximal end of the barrier portion, and the barrier portion and the covering section form a housing which houses a part of the base of the nearest tube on the side of the end wall. an inlet-side tank having an inlet port for leading the target fluid into the inlet-side tank therethrough; an outlet-side tank having an outlet port for leading the target fluid out of the outlet-side tank therethrough; and a plurality of tubes (4A to 4D) each extending from the inlet-side tank to the outlet-side tank, wherein: at least one of the inlet-side tank and the outlet-side tank comprises: a sidewall (6; 9) extending along a given axis (J1; J2) and surrounding the axis; and an end wall (7, 8; 10, 11) closing an opening at an end of the sidewall in a longitudinal direction of the tank along the axis; the plurality of tubes are fixed to the sidewall in a state in which they penetrate through the sidewall via respective ones of a plurality of through-holes formed in the sidewall in such a manner as to be arrayed in a line along the longitudinal direction, the heat exchanger further comprises a protective member fixed to the sidewall to protect a nearest tube (4A, 4D) nearest to the end wall among the plurality of tubes, the protective member having a barrier portion interposed between the end wall and an end portion of the nearest tube disposed inside the sidewall, and the protective member has a covering section extending from a distal end of the barrier portion toward the side away from the end wall, characterized in that the protective member has a pair of fixing sections extending from the covering section, respectively, toward opposite sides in a direction orthogonal to the longitudinal direction of the tank, for fixing the protective member to the sidewall, a small gap is formed between the sidewall and the proximal end of the barrier portion, and the barrier portion and the covering section form a housing which houses a part of the base of the nearest tube on the side of the end wall. at least one of the inlet-side tank and the outlet-side tank comprises: a sidewall (6; 9) extending along a given axis (J1; J2) and surrounding the axis; and an end wall (7, 8; 10, 11) closing an opening at an end of the sidewall in a longitudinal direction of the tank along the axis; the plurality of tubes are fixed to the sidewall in a state in which they penetrate through the sidewall via respective ones of a plurality of through-holes formed in the sidewall in such a manner as to be arrayed in a line along the longitudinal direction, the heat exchanger further comprises a protective member fixed to the sidewall to protect a nearest tube (4A, 4D) nearest to the end wall among the plurality of tubes, the protective member having a barrier portion interposed between the end wall and an end portion of the nearest tube disposed inside the sidewall, and the protective member has a covering section extending from a distal end of the barrier portion toward the side away from the end wall, characterized in that the protective member has a pair of fixing sections extending from the covering section, respectively, toward opposite sides in a direction orthogonal to the longitudinal direction of the tank, for fixing the protective member to the sidewall, a small gap is formed between the sidewall and the proximal end of the barrier portion, and the barrier portion and the covering section form a housing which houses a part of the base of the nearest tube on the side of the end wall.