Disclosed is a method for detecting lipid bilayer membrane particles or fragments thereof, having predetermined molecules existing on surfaces thereof, in a biological sample collected from a subject, the method comprising: adding to the biological sample a dye that stains a lipid bilayer membrane; adding a substance that specifically binds to the predetermined molecules; trapping the substance bound to the predetermined membrane molecules and separating unbound components; and detecting the separated stained lipid bilayer membrane particles or fragments thereof by measurement of the dye emission spectrum. The specific binding substance is conjugated to a magnetic bead or binds to a magnetic bead, the trapping and separating steps are performed magnetically, and the particle size of the magnetic bead is equal to or less than the minimum detection sensitivity of the measurement system.