Abstract: A substrate detecting apparatus includes: a light sensor unit having a light-emission element and a light-receiving element arranged to face each other across the cassette, and a vertical driving device for moving at least one of the light sensor unit and the cassette relative to each other in a vertical direction a substrate position detecter is also provided for detecting a vertical positional range of each substrate held in the cassette, based on a wave form of an output signal generated by the light sensor unit as the at least one of the light sensor unit and the cassette is vertically moving relative to each other. A substrate conveying apparatus includes a clearance measurement device for measuring a vertical clearance between a pair of substrates held in the cassette, and an arm driving device for inserting the conveyance arm between the pair of substrates while lifting up the conveyance arm along a slant locus when the vertical clearance is less than a predetermined critical value.