The present invention provides a microfluidic device which is molded with a die and has a specimen inlet part. The microfluidic device has the specimen inlet part. The specimen inlet part has an inlet channel for introducing a specimen into the flow channel, wherein the inlet channel has a diameter which continuously and gradually increases as the inlet channel approaches the flow channel, or has a diameter which is constant in the vicinity of an inlet port and then continuously and gradually increases as the inlet channel approaches the flow channel.