to a first embodiment of the present invention will be described below with reference to fig1 and 2 as shown in fig1 an in vivo examination apparatus 1 according to this embodiment includes an optical unit 4 having a laser light source 2 and an optical detector 3 an optical fiber 5 that transmits laser light from the laser light source 2 and fluorescence towards the optical detector 3 a measurement head 6 that two dimensionally scans the laser light transmitted by the optical fiber 5 and an insertion part 9 that is supported so as to be rotatable about a longitudinal axis thereof by means of a bearing 8 in a casing 7 of the measurement head 6 the optical unit 4 includes a dichroic mirror 10 that transmits excitation light from the light source 2 and that reflects fluorescence returning from the living organism a focusing lens 11 that focuses the laser light onto the tip of the optical fiber 5 and a focusing lens 12 that focuses the fluorescence reflected by the dichroic mirror 10 onto the optical detector 3 the measurement head 6 includes a collimator lens 13 for converting the laser light transmitted by the optical fiber 5 into a collimated beam a galvano mirror optical scanning unit 14 that two dimensionally scans the collimated beam a pupil projection lens 15 that forms an intermediate image of the beam scanned by the galvano mirror 14 an imaging lens 16 that gathers the light forming the intermediate image and a focusing lens 17 that.