A measuring method and apparatus in which a measurable object (23) is irradiated with acoustic waves to measure a change in property value of charged particles in the object from electromagnetic waves induced thereby. A part (2) of the measurable object irradiated with an acoustic focused beam (1) is in a charge distribution state in which positive charged particles (3) are greater in number in the part (2) where electromagnetic waves induced by positive charged particles (3) are not canceled by those induced by negative charged particles (4) and where net electromagnetic waves (6) are induced. Since a change in concentration of positive charged particles (3) and/or negative charged particles (4) changes the intensity of electromagnetic waves (6), it is possible to know such a change in concentration of the charged particles from a change in intensity of electromagnetic waves (6).