Abstract: Disclosed is a simple device for a membrane assay using the lateral flow immunoassay method, whereby a subject to be detected can be detected at a high sensitivity, provided with, as a label drying pad, a substrate which has a higher tensile strength than glass fiber and can well release a label. The present invention provides a simple membrane assay device, comprising: a supporting board, a sample supply part, a label containing a labeling component which labels a subject to be detected, a development part formed with a detection part which includes a trapping reagent for detecting or quantifying the subject to be detected, and an absorption part, wherein a non-woven fabric which includes fibers having a fiber diameter of 0.05 to 10 ?m is used in the labeling component part.