This article aims at studying pseudo construction of student thinking in mathematical concepts, integer number operation, algebraic forms, area concepts, and triangle concepts. 391 junior high school students from four districts of East Java Province Indonesia were taken as the subjects. Data were collected by means of distributing the main instrument and tracer instrument to the subjects respectively. Both instruments were deployed for the purpose of digging up the construction process. The construction was clustered on the basis of the pseudo construction cases and followed with in-depth interviews to three subjects of each case. The findings show that pseudo construction was identified in four cases. The first case was associated with integer operations, operations of algebraic form, the concept of area, and the concept of triangle. They used analogy of "in debt" to construct concepts of negative number operation. In the second case, they used objects (book, pencil, and thing) to describe variables in the algebraic form operation. For the third case, students deciphered unit area (m[superscript 2]) as multiplication m x m. In the fourth case, students did not pay attention to the requirements of the triangle. Although they gave a right answer to their work, their construction concept was completely false.