Building a small garden wall and unsure which technique to use
Your use of metric measurements leads me to believe you're not in the US. That aside, most US big-box home improvement stores carry retaining wall blocks that are designed to interlock. I'm sure there is something similar where you live. 

This website (hosted by a US-based big-box store (no endorsement expressed or implied) has a short tutorial on how to build a block retaining wall roughly .4m tall. Similar techniques could be used to build one a bit higher. Depending on the block you use, you may be able to build taller.

These are instructions for using a block that has a lip on the back so that each one locks against the one below it to prevent them from sliding forward. Blocks similar to this:

Image sourced from article above

Basically:


Layout your line (yours is a simple straight line)
Trench about 1/2 a block deep
Tamp the ground
Fill with "paver base" (crushed rock that compacts well) and tamp that
Carefully set the first row of block checking each one for level side-to-side and front-to-back, and checking several blocks for level 
Start the 2nd row with a 1/2 block (preferably cut with a power saw &amp; masonry blade, though you could chip it in half with a sledge and cold chisel).
Continue to build the wall up, checking for level.
Lay down some landscape fabric and crushed stone to allow for drainage
Use cement adhesive for the top two rows to help them stay put.
Put some sort of cap stone on as the top layer, if desired, or just let the block run to the top.


Of course, this type of wall may not meed code for your locale, so you'd have to check on that, but this is a simpler and less expensive method than the "pyramid wall" shown in your drawing, and is quite acceptable in most US jurisdictions.