PROBLEM TO BE SOLVED: To provide a fix planting plate member that can be mutually and smoothly deformed in expansion/contraction between a folded state and an expanded state.SOLUTION: A distance between adjacent plate fragments 8 of a plate fragment 8 group on a lateral second row and fourth row which are arrayed in a longitudinal direction is shorter than a distance between adjacent plate fragments 2 of a plate fragment 2 group on a lateral first row, third row and fifth row which are arrayed in a longitudinal direction. Longitudinal upper folding members 4,10 have: two standing walls 4a,10a which are arranged next to a longitudinal lower folding member 9 in a lateral direction, and stand up in a folded state and a connection part 4b which connects the two standing walls 4a,10a in a longitudinal direction. The two standing walls 4a,10a face each other in a longitudinal direction with a gap in a folded state by the connection part 4b. The longitudinal lower folding member 9, when a lateral folding member 3 is folded in a folded state, passes through the gap of the two standing walls 4a,10a and slides along a lateral direction.
