PROBLEM TO BE SOLVED: To provide a probe for measuring electrical activity of a brain by reliably applying optical stimulation to target cells and injecting a liquid medicine.SOLUTION: A probe 21 according to the present invention, which has an arc shape embracing an optical fiber 14 in such a manner as to cover at least a semicircular length of an outer peripheral length of the optical fiber 14, includes an optical fiber guide groove 22 that is provided in parallel with a longitudinal direction of the probe 21 on the outer periphery of the probe 21, and at least one metal wire that is arranged in a longitudinally juxtaposed manner.
