A proximity detecting device includes: a first detection electrode group having detection electrodes; a second detection electrode group having detection electrodes that orthogonally cross the first detection electrode group; an obliquely crossing detection electrode group having detection electrodes that orthogonally cross the first and second detection electrode groups; a detector capable of detecting electrostatic capacitances of each of the first and second detection electrode groups and the obliquely crossing detection electrode group; and a controller that performs detection through switching between a first detection mode in which a proximity state of a detection-target object is determined based on the electrostatic capacitances of the first and second detection electrode groups and a second detection mode in which a proximity state of each of a plurality of detection-target objects is determined based on the electrostatic capacitances of the first and second detection electrode groups and the obliquely crossing detection electrode group.