A microfluidic device (1,100,100a,100b,100c) for detecting a target gene, comprising: a sample chamber adapted to contain sample solution; a microchannel which is connected to the sample chamber through which the sample solution flows; and a microbead packing (30,140,140a,140b,140c,140d,140e) arranged on a flow path of the sample solution in the microchannel; wherein the microbead packing (30,140,140a,140b,140c,140d,140e) comprises: a packing tube (31,145) arranged at a microchannel so as to partially constitute the flow path of the sample solution, a plurality of microbeads (32,141) contained in the packing tube (31,145) and being in close contact with each other to form voids between the microbeads (32,141), and probe linkers formed on a surface of each microbead (32,141), wherein the probe linkers are configured to amplify a target gene in the sample solution by complementary bonding with the target gene, thereby detecting the target gene, characterized by further comprising a negative pressure chamber arranged on the opposite side of the sample chamber to be in fluid communication with the microchannel, the negative chamber being arranged to apply negative pressure from outside to make the sample solution flow through the microchannel, which is arranged so that the void is blocked or a size of the void is reduced by the amplification of the target gene induced by the complementary bonding between the target gene and the probe linker, whereby the target gene is detected according to a change of the negative pressure applied by the negative pressure chamber, wherein the sample chamber, the microchannel and the microbead packing (30,140,140a,140b,140c,140d,140e) are provided in plural, respectively to be arranged in parallel and the microbeads contained in one of the microbead packings (30,140,140a,140b,140c,140d,140e) do not have the probe linkers. a sample chamber adapted to contain sample solution; a microchannel which is connected to the sample chamber through which the sample solution flows; and a microbead packing (30,140,140a,140b,140c,140d,140e) arranged on a flow path of the sample solution in the microchannel; wherein the microbead packing (30,140,140a,140b,140c,140d,140e) comprises: a packing tube (31,145) arranged at a microchannel so as to partially constitute the flow path of the sample solution, a plurality of microbeads (32,141) contained in the packing tube (31,145) and being in close contact with each other to form voids between the microbeads (32,141), and probe linkers formed on a surface of each microbead (32,141), wherein the probe linkers are configured to amplify a target gene in the sample solution by complementary bonding with the target gene, thereby detecting the target gene, characterized by further comprising a negative pressure chamber arranged on the opposite side of the sample chamber to be in fluid communication with the microchannel, the negative chamber being arranged to apply negative pressure from outside to make the sample solution flow through the microchannel, which is arranged so that the void is blocked or a size of the void is reduced by the amplification of the target gene induced by the complementary bonding between the target gene and the probe linker, whereby the target gene is detected according to a change of the negative pressure applied by the negative pressure chamber, wherein the sample chamber, the microchannel and the microbead packing (30,140,140a,140b,140c,140d,140e) are provided in plural, respectively to be arranged in parallel and the microbeads contained in one of the microbead packings (30,140,140a,140b,140c,140d,140e) do not have the probe linkers. a packing tube (31,145) arranged at a microchannel so as to partially constitute the flow path of the sample solution, a plurality of microbeads (32,141) contained in the packing tube (31,145) and being in close contact with each other to form voids between the microbeads (32,141), and probe linkers formed on a surface of each microbead (32,141), wherein the probe linkers are configured to amplify a target gene in the sample solution by complementary bonding with the target gene, thereby detecting the target gene, characterized by further comprising a negative pressure chamber arranged on the opposite side of the sample chamber to be in fluid communication with the microchannel, the negative chamber being arranged to apply negative pressure from outside to make the sample solution flow through the microchannel, which is arranged so that the void is blocked or a size of the void is reduced by the amplification of the target gene induced by the complementary bonding between the target gene and the probe linker, whereby the target gene is detected according to a change of the negative pressure applied by the negative pressure chamber, wherein the sample chamber, the microchannel and the microbead packing (30,140,140a,140b,140c,140d,140e) are provided in plural, respectively to be arranged in parallel and the microbeads contained in one of the microbead packings (30,140,140a,140b,140c,140d,140e) do not have the probe linkers.