The present invention provides a nanomechanical sensor in which a negative influence of water in a sample on measurement is suppressed. In an embodiment of the present invention, as a receptor material of the nanomechanical sensor, a low-hygroscopic material such as polysulfone, polycaprolactone, poly(vinylidene fluoride), or poly(4-methylstyrene) is used. According to this embodiment, a negative influence, such as saturation of a receptor layer by water in the sample, or masking of an output signal based on trace components by an output signal based on water contained in the sample in a large amount, can be suppressed.