A device for reading an assay test result on a test carrier comprises: a light-emitting element (5) for emitting and irradiating light onto corresponding one or more zones of the test carrier (3); a light-blocking element (12) for blocking the light mirror-reflected by the test carrier (3) from being irradiated on a photodetector (7); and a window (10), through which the light emitted from the light-emitting element (5) is irradiated onto the corresponding zones of the test carrier (3). In one preferred embodiment, the positions of the light-emitting element (5), the light-blocking element and the window (10) meet the function of S3≦>2*S7−S7*S2/S1, where S1 represents the vertical distance between the light-emitting element and the window; S2 represents the vertical height of the light-blocking element; S3 represents the vertical distance between the light-blocking element and the light-emitting element; and S7 represents the length of the window.