Disclosed herein is an optical organism measuring apparatus in which cables provided on both light transmission and receiving sides are sufficiently reduced in diameter and provided with flexibility for attaining handleability while light can be transmitted and received in high efficiency so that information can be obtained from a deep portion in an organism. Semiconductor lasers (2-1, 2-2, 2-3) are coupled with incident ends of a plurality of single core optical fibers which are contained in a flexible probe (12), so that laser light guided by the single core optical fibers is applied to an organism (8) from a forward end portion of the probe (12). A light receiving probe (18) is provided on its forward end with a silicon photodiode (14), which is attached in close contact to the organism (8) to receive light transmitted through or reflected by the organism (8). This silicon photodiode (14) is integrated with a preamplifier (16). A cable for transmitting a detection signal which is amplified by the preamplifier (16) is formed by a flexible shielding wire.