An apparatus for measuring biopermeability is disclosed. The apparatus includes a frame, a light source, a light-receiving element, a pre-amplifier, an off-set adjustment amplifier and a DC volt meter. The light source and light-receiving element are secured to the frame such that they face each other while keeping a gap therebetween such that an organism under measurement can be received in the gap without being urged. The pre-amplifier is connected to the light-receiving element and has a gain switching function. The summing amplifier is connected for zero adjustment and gain adjustment to the output side of the pre-amplifier and has an output terminal from which a DC data representing biopermeability is provided. Between the output terminal and ground the DC volt meter is connected.