A low energy electron diffraction - i.e. LEED-detection module, comprising: a first vacuum chamber having an aperture at one end for receiving diffracted electrons from a specimen that is irradiated with a probe beam of electrons; a second vacuum chamber connected to the first vacuum chamber at one end thereof to receive the diffracted electrons that have been transported through the first vacuum chamber, a dimension of the second vacuum chamber in a direction perpendicular to a travelling direction of the diffracted electrons being larger than a corresponding dimension of the first vacuum chamber; a two-dimensional electron detector (104,116) disposed in the second vacuum chamber at an end opposite to said one end of the second vacuum chamber to which the first chamber is connected, to detect the diffracted electrons; a potential shield made of electrically conductive material disposed generally along an inner surface of the first vacuum chamber and an inner surface of the second vacuum chamber, the potential shield being configured to be applied with a first acceleration voltage to accelerate and focus the diffracted electrons from the specimen; a magnetic lens disposed adjacent to a place where the first vacuum chamber is connected to the second vacuum chamber to expand a beam of the diffracted electrons that have been transported through the first vacuum chamber towards the two-dimensional electron detector; and a generally plane-shaped energy filter to repel electrons having an energy lower than the probe beam of electrons that impinges on the specimen, the energy filter being disposed to have a gap with respect to the potential shield and being configured to be applied with a second acceleration voltage (111,112) to collimate the beam of the diffracted electrons expanded by the magnetic lens. a first vacuum chamber having an aperture at one end for receiving diffracted electrons from a specimen that is irradiated with a probe beam of electrons; a second vacuum chamber connected to the first vacuum chamber at one end thereof to receive the diffracted electrons that have been transported through the first vacuum chamber, a dimension of the second vacuum chamber in a direction perpendicular to a travelling direction of the diffracted electrons being larger than a corresponding dimension of the first vacuum chamber; a two-dimensional electron detector (104,116) disposed in the second vacuum chamber at an end opposite to said one end of the second vacuum chamber to which the first chamber is connected, to detect the diffracted electrons; a potential shield made of electrically conductive material disposed generally along an inner surface of the first vacuum chamber and an inner surface of the second vacuum chamber, the potential shield being configured to be applied with a first acceleration voltage to accelerate and focus the diffracted electrons from the specimen; a magnetic lens disposed adjacent to a place where the first vacuum chamber is connected to the second vacuum chamber to expand a beam of the diffracted electrons that have been transported through the first vacuum chamber towards the two-dimensional electron detector; and a generally plane-shaped energy filter to repel electrons having an energy lower than the probe beam of electrons that impinges on the specimen, the energy filter being disposed to have a gap with respect to the potential shield and being configured to be applied with a second acceleration voltage (111,112) to collimate the beam of the diffracted electrons expanded by the magnetic lens.