To provide a bioelectrode having a structure which ensures electrical contact between the scalp of a subject and an electrode and never gives pains to the subject by the contact in the bioelectrode which is used in measuring brain waves and has a dry structure.

In a bioelectrode 1, when external force (external force means force that acts when a metal probe 5 is brought into contact with a scalp) does not acts on the metal probe 5 as shown in Fig.2(A), a spring 4 biases the metal probe 5 in a direction of the arrow A in the same Fig.(A). At the moment, a flange 5b of the metal probe 5 locks on a flange 6a of a casing 6 and prevents the metal probe 5 from dropping. Meanwhile, as shown in the same Fig.(B), when external force acts on the metal probe 5, the locking is released, and the metal probe 5 resists against biasing force of the spring 4 and moves inside the casing 6 in a direction of an arrow B in the same Fig.(B) for example, in such a form that the flange 5b of the metal probe 5 is guided by an inner circumference surface 6b of the casing 6.