An apparatus for measuring radon and thoron using an ionization chamber, the apparatus comprising: a pump for air inflow suctioning and sending external air to at least one channel; a first sensor module for receiving the air sent from the pump for air inflow through a first gas line in the first channel, and outputting an alpha particle detection signal of an electrical signal by detecting alpha (α) particles discharged from radon and thoron included in the air flowing in an ionization chamber having a predetermined size; an air inflow delay module for receiving the air sent from the pump for air inflow through a second gas line in a second channel, delaying the air for a predetermined delay time, and then outputting the air; a second sensor module for receiving air output from the air inflow delay module and outputting an alpha particle detection signal of an electrical signal by detecting alpha (α) particles discharged from radon and thoron included in the air flowing in the ionization chamber having a predetermined size; and a control module for receiving in real time - alpha particle detection signals of electrical signals output from the first and second sensor modules as waveforms, configured to compare and analyse the waveforms output from the first module and the second module with signal pattern information data according to external noise signal types stored in advance, configured to discriminate normal or abnormal alpha particle detection signals, configured to count the normal alpha particle detection signals discriminated for a predetermined measurement time, and configured to calculate radioactive ray concentration values on the basis of the counted number of times of the normal alpha particle detection signals, characterized in that the air inflow delay module is configured by stacking up and down a plurality of cases each having a predetermined space such that air flowing therein stay for a predetermined time, and at least one hole is formed between the stacked cases to be able to pass the air, the first gas line connects the pump for air inflow to the first sensor module, the second gas line connects the pump for air inflow to the air inflow delay module, the pump for air inflow is configured to be continuously operated and to deliver air to the first sensor module within about 5 seconds through only the common first gas line and to deliver air to the second module with a delay of about 5 minutes. a pump for air inflow suctioning and sending external air to at least one channel; a first sensor module for receiving the air sent from the pump for air inflow through a first gas line in the first channel, and outputting an alpha particle detection signal of an electrical signal by detecting alpha (α) particles discharged from radon and thoron included in the air flowing in an ionization chamber having a predetermined size; an air inflow delay module for receiving the air sent from the pump for air inflow through a second gas line in a second channel, delaying the air for a predetermined delay time, and then outputting the air; a second sensor module for receiving air output from the air inflow delay module and outputting an alpha particle detection signal of an electrical signal by detecting alpha (α) particles discharged from radon and thoron included in the air flowing in the ionization chamber having a predetermined size; and a control module for receiving in real time - alpha particle detection signals of electrical signals output from the first and second sensor modules as waveforms, configured to compare and analyse the waveforms output from the first module and the second module with signal pattern information data according to external noise signal types stored in advance, configured to discriminate normal or abnormal alpha particle detection signals, configured to count the normal alpha particle detection signals discriminated for a predetermined measurement time, and configured to calculate radioactive ray concentration values on the basis of the counted number of times of the normal alpha particle detection signals, characterized in that - alpha particle detection signals of electrical signals output from the first and second sensor modules as waveforms, configured to compare and analyse the waveforms output from the first module and the second module with signal pattern information data according to external noise signal types stored in advance, configured to discriminate normal or abnormal alpha particle detection signals, configured to count the normal alpha particle detection signals discriminated for a predetermined measurement time, and configured to calculate radioactive ray concentration values on the basis of the counted number of times of the normal alpha particle detection signals, characterized in that the air inflow delay module is configured by stacking up and down a plurality of cases each having a predetermined space such that air flowing therein stay for a predetermined time, and at least one hole is formed between the stacked cases to be able to pass the air, the first gas line connects the pump for air inflow to the first sensor module, the second gas line connects the pump for air inflow to the air inflow delay module, the pump for air inflow is configured to be continuously operated and to deliver air to the first sensor module within about 5 seconds through only the common first gas line and to deliver air to the second module with a delay of about 5 minutes.