A tubular heat exchanger comprising: an outer jacket through which in use of the tubular heat exchanger a heat medium is introduced and discharged; a combustion chamber coupled to the inside of the outer jacket so that a heat medium passage is formed between the combustion chamber and the outer jacket, and configured to perform combustion of a burner; a plurality of tubes formed in a flat shape configured to allow combustion gas, which is generated in the combustion chamber, to flow along the inside of the plurality of tubes and exchange heat with the heat medium; and a turbulator coupled to the inside of the tubes configured to induce generation of turbulence in a flow of the combustion gas, the tubular heat exchanger characterized in that the turbulator includes a flat part configured to divide an inner space of the tube into two portions and disposed in a longitudinal direction of the tube, and a plurality of first guide portions and second guide portions spaced apart from both side surfaces of the flat part along a longitudinal direction and formed to alternatively protrude to be inclined; the first guide portion is disposed on one side surface of the flat part to be inclined to one side; the second guide portion is disposed on the other side surface of the flat part to be inclined to the other side; and whereby in use of the tubular heat exchanger each of the heat media introduced into the first guide portion and the second guide portion is sequentially transferred to the second guide portion and the first guide portion disposed adjacent to an opposite side of the flat part to alternatively flow through both spaces of the flat part; the turbulator includes an upper turbulator provided at a side into which the combustion gas is introduced, and a lower turbulator provided at a side from which the combustion gas is discharged; and an interval in which the plurality of first guide portions and the plurality of second guide portions formed in the lower turbulator are vertically spaced apart from each other is disposed at a relatively denser interval than an interval in which the plurality of first guide portions and the plurality of second guide portions formed in the upper turbulator are vertically spaced apart from each other for corresponding to changes in temperature and volume of the combustion gas passing through the tubes. an outer jacket through which in use of the tubular heat exchanger a heat medium is introduced and discharged; a combustion chamber coupled to the inside of the outer jacket so that a heat medium passage is formed between the combustion chamber and the outer jacket, and configured to perform combustion of a burner; a plurality of tubes formed in a flat shape configured to allow combustion gas, which is generated in the combustion chamber, to flow along the inside of the plurality of tubes and exchange heat with the heat medium; and a turbulator coupled to the inside of the tubes configured to induce generation of turbulence in a flow of the combustion gas, the tubular heat exchanger characterized in that the turbulator includes a flat part configured to divide an inner space of the tube into two portions and disposed in a longitudinal direction of the tube, and a plurality of first guide portions and second guide portions spaced apart from both side surfaces of the flat part along a longitudinal direction and formed to alternatively protrude to be inclined; the first guide portion is disposed on one side surface of the flat part to be inclined to one side; the second guide portion is disposed on the other side surface of the flat part to be inclined to the other side; and whereby in use of the tubular heat exchanger each of the heat media introduced into the first guide portion and the second guide portion is sequentially transferred to the second guide portion and the first guide portion disposed adjacent to an opposite side of the flat part to alternatively flow through both spaces of the flat part; the turbulator includes an upper turbulator provided at a side into which the combustion gas is introduced, and a lower turbulator provided at a side from which the combustion gas is discharged; and an interval in which the plurality of first guide portions and the plurality of second guide portions formed in the lower turbulator are vertically spaced apart from each other is disposed at a relatively denser interval than an interval in which the plurality of first guide portions and the plurality of second guide portions formed in the upper turbulator are vertically spaced apart from each other for corresponding to changes in temperature and volume of the combustion gas passing through the tubes.