Provision of a biological information detecting device capable of stably detecting a biological signal in good condition. A device body, a pair of electrode portions 26A and 26B provided in the device body and respectively contacting a biological surface and a band-shaped fixing band 30 for covering the pair of electrode portions 26A and 26B and fixing the device body to a body are provided, and a guide portion 40A which allows relative movement between each of the electrode portions 26A/26B and the fixing band 30 in an extending direction of the fixing band 30 and restricts movement in a width direction orthogonal to the extending direction is arranged between each of the electrode portions 26A/26B and the fixing band 30.