To provide a multilayer fiber structure which is low in pressure loss, excellent in delamination or suppressed in ultrafine fiber, and a filter medium comprising the multilayer fiber structure.

The multilayered fiber structure comprises at least three layers of a lower layer, an intermediate layer and an upper layer. The intermediate layer is the fiber structure comprising the ultrafine fiber having a diameter of 10-500 nm, and the upper and lower layers are nonwoven fabrics comprising fibers having diameters of 1-100 μm. The upper layer and the lower layer are partially thermocompression-bonded by embossing in a cross section of a recessed part formed by the thermocompression-bonding, the upper opening is larger than a bottom, and an angle θ formed of a tangent contacting with the side surface of the recessed part and the bottom part is 140-170°.