A photoelectric sensor (1; 1a; 1b; 1c) that is a transmissive photoelectric sensor or a retro-reflective photoelectric sensor for use in combination with a retro-reflective member, comprising: light projecting means configured to emit detection light for detecting a detection object that is present in a detection region; light receiving means configured to receive the detection light from the detection region; determination means configured to determine whether or not the detection object is present by comparing a received light signal value, which is an output signal value of the light receiving means, with a threshold; received light signal adjustment means that includes an operation unit having an operable range within which the operation unit is configured to be operated to adjust at least one sensitivity parameter of projection light power and received light gain within a predetermined range, and a first adjustment unit configured to adjust, by an operation of the operation unit from one end to the other of the operable range, the at least one sensitivity parameter so that a ratio of the maximum value to the minimum value of the received light signal value is not greater than 2.6; and sensitivity parameter adjustment means that includes a trigger input reception unit, and a second adjustment unit configured to adjust at least one of the projection light power, the received light gain, and the threshold when the trigger input reception unit receives a trigger input while the operation unit is located at a predetermined position in a state in which the detection object is not present in the detection region, wherein the second adjustment unit is configured to adjust at least one of the projection light power, the received light gain, and the threshold so that the threshold is between the maximum value and the minimum value of the received light signal value, and so that the first adjustment unit comprises an adjustment range being a predetermined range that is included between 50% and 130% in terms of a ratio of the threshold to the received light signal value. light projecting means configured to emit detection light for detecting a detection object that is present in a detection region; light receiving means configured to receive the detection light from the detection region; determination means configured to determine whether or not the detection object is present by comparing a received light signal value, which is an output signal value of the light receiving means, with a threshold; received light signal adjustment means that includes an operation unit having an operable range within which the operation unit is configured to be operated to adjust at least one sensitivity parameter of projection light power and received light gain within a predetermined range, and a first adjustment unit configured to adjust, by an operation of the operation unit from one end to the other of the operable range, the at least one sensitivity parameter so that a ratio of the maximum value to the minimum value of the received light signal value is not greater than 2.6; and sensitivity parameter adjustment means that includes a trigger input reception unit, and a second adjustment unit configured to adjust at least one of the projection light power, the received light gain, and the threshold when the trigger input reception unit receives a trigger input while the operation unit is located at a predetermined position in a state in which the detection object is not present in the detection region, wherein the second adjustment unit is configured to adjust at least one of the projection light power, the received light gain, and the threshold so that the threshold is between the maximum value and the minimum value of the received light signal value, and so that the first adjustment unit comprises an adjustment range being a predetermined range that is included between 50% and 130% in terms of a ratio of the threshold to the received light signal value.