A gas detection apparatus using a gas sensor element whose sensor resistance changes in accordance with concentration of a specific gas, comprising: acquisition means for acquiring a sensor output value at predetermined cycle intervals, the sensor output value corresponding to the sensor resistance; and concentration detection means for detecting a change in the concentration of the specific gas and for generating a low concentration signal when the concentration of the specific gas is low and a high concentration signal when the concentration of the specific gas is high, wherein the concentration detection means (S3B) comprises concentration increase detection means for generating the high concentration signal in place of the low concentration signal when, during a period in which the low concentration signal is generated, the sensor output value shifts toward a high concentration direction with respect to a reference value (B(n)) by an amount equal to or greater than a high concentration threshold (Tu, Tu1, Tu2), and concentration decrease detection means (S3C) for generating the low concentration signal in place of the high concentration signal when, during a period in which the high concentration signal is generated, the sensor output value shifts toward a low concentration direction with respect to the reference value by an amount equal to or greater than a low concentration threshold (Td) wherein the concentration increase detection means uses a first high concentration threshold as the high concentration threshold during a sensitized period of the period in which the low concentration signal is generated, the sensitized period following a switching from the high concentration signal to the low concentration signal, and a second high concentration threshold as the high concentration threshold during the remaining portion of the period in which the low concentration signal is generated, and wherein the first high concentration threshold is a value on a sensitivity-increasing-direction side with respect to the second high concentration threshold. acquisition means for acquiring a sensor output value at predetermined cycle intervals, the sensor output value corresponding to the sensor resistance; and concentration detection means for detecting a change in the concentration of the specific gas and for generating a low concentration signal when the concentration of the specific gas is low and a high concentration signal when the concentration of the specific gas is high, wherein the concentration detection means (S3B) comprises concentration increase detection means for generating the high concentration signal in place of the low concentration signal when, during a period in which the low concentration signal is generated, the sensor output value shifts toward a high concentration direction with respect to a reference value (B(n)) by an amount equal to or greater than a high concentration threshold (Tu, Tu1, Tu2), and concentration decrease detection means (S3C) for generating the low concentration signal in place of the high concentration signal when, during a period in which the high concentration signal is generated, the sensor output value shifts toward a low concentration direction with respect to the reference value by an amount equal to or greater than a low concentration threshold (Td) wherein the concentration increase detection means uses a first high concentration threshold as the high concentration threshold during a sensitized period of the period in which the low concentration signal is generated, the sensitized period following a switching from the high concentration signal to the low concentration signal, and a second high concentration threshold as the high concentration threshold during the remaining portion of the period in which the low concentration signal is generated, and wherein the first high concentration threshold is a value on a sensitivity-increasing-direction side with respect to the second high concentration threshold.